Hey welcome, and congratulations on driving the right sort of car
looking through your thread so far a few things spring to mind..
1. The Eta diff (2.93) is too long to work correctly with the m40/m42 4cylinder engines- Ideal ratio for them would be about 3.64 if you didnt mind losing some accelleration
2. If you used an m42 out of an early (pre 1996) e36 (92 onward) the gearbox has a 1:1 5th so would work with the 2.93.
3. The ideal setup for a 2.93 diff would be to build a 2.7 stroker m20 engine- Basically use the 525e (eta) bottom end with a 2.0 m20 head. This would give you approx 180BHP, and a torque curve that starts at 1000rpm- and levels off at max torque from 1700-6000rpm. Essentially build a torque monster to pull that diff. Several folk I know of manage 35+ UK MPG with "Spirited" driving using this setup.
4. 13" wheels will not clear standard e30 Discs/calipers on the car. Minimum wheel size is 14". Car came as standard with 195/65/r14 on the 14" bottle top alloys. I'd suggest fitting 195/50/15- gives a smaller rotating mass, better steering feel and cheap tyres
5. Oil cooler removal on the m20 is simple- just fit the oil filter adapter from a 2.0 m20- It doesnt have the takeoff for the cooler pipes. Cooler itself is a couple of bolts in the front valance and 2x 24mm fittings at the oil filter.
6. if you're doing the rear beam- Please fit Genuine BMW (Lemfroder) bushes. They last better than anything else,a dn its such a pig of a job to do..
7. The e30's biggest issue is its cD of 0.36 compared to the e36's cD of 0.30, so time invested in cleaning up the aero should pay off hansomely- especially if pulsing and gliding at higher speeds
8. I'm happy to source and ship any bits you may need- e.g. m42 engines/2.0 m20 heads/oil filter bits etc, as as far as I can see you dint get either of these cars over there?
keep up the good work though- more folks shourld drive these rather than 3.8v6 FWD trash that seems to be the marketplace norm over in the US!
Neil