...to help you make the drivetrain choise easy? :
Seek for drivetrains from front-wheel-drive cars that has a lightweight engine(alloy) which is known to be durable, and preferably with some tuning potential. You choose the power and volume from your needs (Ferrari says that a sportscar should have at least 200hp per 1000 kilogram....)
This engine should be mated with an alloy gearbox with gear-ratios suitable for the cars weight, wheel-sizes, the engines caracteristics and what you intend to use the car for (everyday or racing, maybe something in between?).
Now is the time to check if there is room for your choices, I measured the Murena 2.2 drivetrain, and it is about 102 cm measured lateral WITH NO EXTRA ROOM TO USE !! Then you have to consider engine mounts, tubing/piping, gearlever....
In my opinion there is a little too small room for a turbo in the engine bay(heat buildup), but on the other hand the turbo-way is the quickest way to get power IF you can handle the engine control unit, which should to be reprogrammed if you change anything from stock (exhaust pipes, for instance...)
..Many details to consider, my choice was the 405MI16 drivetrain with the XU9J4 - D6C (1.9litre 163hp) engine because it is light, durable, there is tuning parts available(intake, camshaft, exhaust, porting) and it comes with a gearbox that suit my needs...It has a Bosch EFI-system... AND it fits in a Murena.
On the minus-side :
It tilts backwards, the ideal would have been some forward tilt to help the weight distribution and to get most of the weight between the wheel axles.
It was hard to find (but I had some luck and found one with 126000km on the clock, the price was EUR1600 for a complete drivetrain with EFI and driveshafts, only missing fuel pump and TDC-sensor to get it going)
Expensive distributor cap, the price in Norway is about EUR100.
Don't let any of this restrict your choices, there are lots of drivetrains to consider, maybe you would like something from Alfa Romeo, VW/Audi, SAAB or Opel???All of these have been fitted in Murenas, and there are plenty of others waiting...
I'm sure that other users on this forum can give you more help in choosing the right drivetrain, after all, I have not installed mine yet...
Good luck, please keep on posting in this forum !