what about using the gearbox from a vauxhall omega
im using an omega as a donor im using the x20xev engine (not too distant relative of the c20xe ) the gearbox is the same stud pattern my gearbox is capable of coping up to 250nm the ones off the 3.0 v6 will cope with 280nm then have your prop made to suit the rear diff you plan to use.
hope thats of some help oh and the gearbox fits into a fairly std chassis ive only tweeked the trans tunnel slightly