I've been told its far too hard but looking at this German build thread it appears an m73 will fit in the hole without further cutting.
http://www.bmw-syndikat.de/bmwsyndikatfotos/topic40640_E36_350i_V12_3er_BMW_-_E36.html
Is anyone able to shed any light on this? From the pics it looks like he has a custom front subframe, but that's not a huge obstacle.
My reason for asking is I can get a tidy 328i coupe with a crook trans very cheaply and there is a cheap M73 on trademe with trans, wiring,