FYI...the motor in a 745i is either an M102 (3.2l) engine with L-jet (found in '82 E23's) and the later motors are M106(3.4l)/Motronic setup-- far more tweakable.
Also, be sure the transmission is in top shape, these things are famous for killing clutch packs if revved in neutral.
There are some guys boosting M30's, especially in the US. TCD (Turbo Charging Dynamics... www.turbochargingdynamics.com
) has several kits for M30's.
Found this on the E12 board...
"We did the conversion on an e28 but instead of using the 745 block we just took all the turbo bits off the engine and bolted them to a 3.5 M30 block. Running 8psi. Cost $750 for the bits and $500 for seals, lines, I/C, oil cooler.
Used an I/C from a SAAB, oil cooler from a Mazda RX-7. Just need to modify the turbo down pipe, modify the passenger side motor mount and make a turbo oil return to the block. An e12 will be easier than an e28 as you don't have to relocate the ABS for the I/C and I don't think the down pipe will interfere with the suspension at all. "
On another thread I found this...
"Just finishing it up on an 1985 e28. Took all the turbo pieces from a 1982 745i and put it on a rebuilt M30 low compression motor. Main challenges are clearance for the turbo/wastegate on the passenger side as well as modifying the downpipe from the wastegate to clear the suspension mounting point. If you use a non-turbo head you need to drill out the threads for the exhaust manifold or get long studs which will fit the stock holes. Other things are:
Drilling the block for the oil return, installing a oxygen sensor, relocating the ABS pump (if you have one), installing an M5 clutch."
More info can be found here.... http://bmwturbos.scottiesharpe.com/default.asp
Remember one thing...rebuilding (highly recommended for durability) one of these 745i motors will cost you some good coin as it is a 'Euro' motor which = $$$.
As pointed out earlier, you can take the Turbo bits and plant them onto an M30 (rebuild recommended). If you want boost, I'd go this way as M30 engine bits are less expensive compared to the M102 and M106 Euro bits if something were to go wrong down the road.
However the advantage of using the M102 or M106 engine is that these motors were meant for Turbo's and engineered to accept the pressure BMW regulated for extended engine life.
You know how it goes...modify/adjust the Turbo pressure etc...= less engine life, but more satisfaction in the short term
Hope this helps you make your decision!