In reply to mad_machine:
In addition to the shock towers, the entire front suspension is different- control arms, struts, etc.
The oil pan is different and unique to the IX for those model years to accommodate the front differential and drive shafts. Euro-spec e34 525ix oil pans will fit. Good luck finding one.
The transmission has a different case to accommodate the transfer case that bolts on the back.
The internals of the manual transmission are supposed to be identical.
Edit: Also, the front sub-frame is aluminum and also has different mount points.
Automatic transmission models have some difference in the transmissions themselves, I forget what it is. There might also be a difference in the ECU.
Final drive ratios were different as well, if I recall correctly.
(edit) Fixed my typo.
If brute force isn't solving your problem, you're not using enough.