you were tyrying to switch to a nissan auto trans and not a th400 or 4l80e? I would not even want to try and swap over a nissan auto into a 5spd. The GM trans swaps are not a bolt up affair either but will yield better results and handle quite a bit of abuse. If it something your dead set on doing I'd go to a GM trans. Just my .02.
" I told my son, you have to catch the football other wise this just looks like child abuse." - My brother