Jim, this was my build plan a few years ago, that's the m30b34 e30 swap.
This is one of the strongest old school engines BMW ever built as a production engine, the m30's powered quite a few different models and quite a few generations.
Dont be fooled by the old school engine, its simple, cheap to maintain, has great HP and torque and it will beat any stock m50 e30 hands down.
It weighs just around 50 lbs more than the m20, weight you can save from removing some stuff from your firewall etc.
The third gen m30b34 produces 211 hp and with some simple cheap mods you can increase this quite a bit. With a good exhaust, MD's software and a nice intake, this engine delivers a fair bit of HP and tons of torque. I have programmed a five speed e34 535i here with the same motor and that car is a beast. At 200 kph it feels like its cruising.
The m50 swap looks cool and is 24 valves but, the m30 performance will eat the pretty m50.
I do like m50's dont get me wrong, just stating the facts as far as simplicity, cost and performance is concerned between the m30 and m50.
SPEED AND POWER IS NOTHING WITHOUT CONTROL,
THANK HITLER, BMW HAS ALL THREE