Its a bitch unless you have done many before, thats why so few people actually do it well, and why it costs, it would work out cheaper, to blow your box and upgrade it.
When you consider you could blow your box, and rebuild it with a tough 1-3rd gears, with standard 4th & 5th, for $3-4000.
then to spend $1-1500 on modding the $1500 nissan box, $650 for a tailshaft, More cross member and tunnel stuffin around, an rb25, barely fits in a commi tunnel, no way you will get inside a standard 86 tunnel, the price for mounts and tunnel mods could be anywhere from $1500-3000 easily.
Its cheaper, easier and quicker to rebuild the crappy sr/RB20 box.
