Much of the information below came from the fine folks on the lotus Europa mailing list.   Accuracy is not guaranteed, use at own risk, etc...   I hope to expand this area over time.

Renault Engine Applications

The two engines that came stock with the Europa are the 821 and 697 series were used in a vast number of Renault models.  The entire engine series comprises 697, 821, 807, and 843 series engines and some potential donors are listed below.  

Renault Engine Specifications

The next table gives the critical dimensions for the rotating bits for various displacements listed above.

*  Measured with flat-topped pistons from piston crown to centre of wrist pin.

Engine type Comparisons

This table compares other aspects of the various engine types. 

Comments

Crossflow vs Wedge

The 821 and 697 engines are generally 'wedge' chambered and have the intake and exhaust on the left side of the engine, while the 807/843 engines are the higher hp, hemi-chambered crossflow types.  The wedge type should be a direct drop-in replacement for the Europa, while the hemi will require at least the fabrication of an exhaust manifold.   

Driving Ancillaries

The R16, Europa and early R15/17s  drove their accessores from a pulley mounted on an extended camshaft at the rear of the engine, while other cars drove them from the a crank-mounted pulley at the front of the engine.    The engine configurations differ in the following respects:

Because of the issues identified above, the ideal donor for a crossflow engine would be an R16 or R17 TS or Gordini with cam-droven  alternator and water pump.

This is an 843 from a 1983 Fuego.  The alternator mounts low and to to the right (in the picture) of the crank pulley.    Smack in the middle of the S2 frame rail.

Crankshafts

All cranks have the same journal sizes, and use the same bearings.  The 1470cc engine has a shorter stroke than the larger engines.    

Pistons and Liners

Pistons are sold typically as sets with cast iron liners.  Liners for 1470 and 1565cc engines mostly have 82.5mm locating base diameters, though some early 697 (not sure if this includes the Lotus 697-04 or just Renault and Mercruiser) engines have locating base diameters of 82mm.  The bore centres are the same.

77mm dia pistons for the 1565cc engines have a 1.5mm lower compression height than their 76mm (1470cc) cousins, to allow for the 3mm longer stroke.  Therefore, pistons and liners must be used with the appropriate crank, but the rods are the same length. 

843 pistons have a 79mm bore and a different wrist pin diameter, thus would need to be used with the correct rods.   Not yet sure about the compression height and rod length.

Connecting Rods

Big and small end diameters and rod length are shared for the 1470cc and 1565 series engines.  Some (all?) 807 rods are more heavily constructed than 697 or 821 rods.  

843 rods have a different small end diameter and are not compatible the other engines.

Camshafts

Camshafts are not interchangeable between wedge (697, 821, 841) and crossflow (807, 842) engines. The valve lobe order is different. Camshafts for wedge heads are exhaust-intake-intake-exhaust-exhaust-intake-intake-exhaust, while crossflow heads alternate between exhaust and intake lobes across the entire head.

The longer-type camshaft is required for installation in a Europa.

Crankcases

Early 697 engines (not sure if these were used on any Europas) used a crankcase with  locating diameters (for the liners) of 82mm.   This dimension later became became 82.5mm, a dimension shared with the 821, 807 and possibly 843 series engines. 

Mounting bosses are identical on 697 and 821 cases, while some 807 and 843 cases may or may not include bosses that permit the use of stock Europa engine mounts.

Cylinder Heads

'Wedge' heads (697, 821, 841) have their intake and exhaust ports on the left side of the engine (in a Europa) and 'crossflow' heads (807,842) have intake ports on the right, exhaust on the left.  697-04 heads differ from the preferred 821-30 head in that the intake ports, while larger, are 'siamesed' for adjacent cylinders and share a common intake runner, while the 821-30 heads have seperate intake passages that continue in the manifold to the common plenum below the carb.

Crossflow (807-13) heads designed for Bosch's D-Jet EFI system have small, elliptical exhaust ports.

Water Pumps

I was looking for water pumps and encountered two different rear-mount pumps available for both the the R16 and R17 1565cc engine. One refers to "1 5/32" mounting" and the other "1 7/16".  This refers to the spacing of the bolts which hold the pulley to the hub. The Europa pulley requires the triangular hub, and the one from my 821,  has a spacing of 1-7/16" between the bolts (NOT bolt circle diameter.  IIRC, if you happen to get the pump with the wrong hub you can press off the hub from your originl and swap them.   

Oil Pumps and Sumps

697 sumps are deeper than later sumps, presumable the oil pickup tube is different as well.

There are two pumps, the smaller (width of rotor) fits the 821 engine and the larger fits the 807 engine.

Renault Gearbox Specifications

Note:  Max hp is at best an estimate, its all about torque/force anyway.  

Gearbox Swaps

Changing to a different gearbox will require significant modifications to the rear chassis crossmember and shift linkage.  Using a NGX box will require suspension mods as well.  Any box taken from a Europa Twin Cam will of course have a different bellhousing, though the box itself will bolt up to a Renault bellhousing.

Gearboxes from the R12,15,16, 17, 18, Fuego and possibly others will bolt to the 821, 807, 843 series of engines.  You will have to solve shifting issues though. Banks Engineering offers some solutions to these issues, and listers have had mixed success with their kits. Gearboxes that will fit include 352, 365,395 NG1, NG3 and with a different bellhousing NG9 which was available here as the Renault Medallion which I believe was known on the continent as maybe R21. 

According to the parts list, the shafts and gears for the 336 and 352 are
the same. The crown wheel and pinion, the housings, and of course the
shifting mechanisms are not.

The 365 and 352 appear very identical, with only the rear casing of the 365
having another shape, necessitating another mounting bracket. Though, on the
inside both the differential, shafts and gears are different. My guess is
that the 365 will take more power than the 352, though I haven't got
anything 'to have it in'.

Differential: 

 2 spider differentials are less durable than their 4 spider cousins.

Stressed shafts:  

Those boxes not capable of operating with their half shafts stressed (as in a stock Europa) require the addition of an upper transverse link on the rear suspension, such as Banks' 'Twin Link" system.

Input Shafts

The NG boxes use different input shafts than the 336/352/365/395 types. The bellhousing has a roller bearing to support it, and the input shaft does not have a "nose" that fits into a pilot bearing in the crank.  The 3xx boxes have a seal instead of a bearing since the input shaft is supported in the crank end.

Bellhousings

The earlier bellhousings are shallower, but will bolt to any
Renault engine thru 843.

NG3 box has a bigger differential, and the bellhousing has a recess to give room to the gear, and less room for the clutch.