1jz swap with a manual tranny will be alot easier in the end in your sc400.
i remember i was looking at doing the 5 spd on my auto sc300.

youve probbly seen these threads but ill list them 4 u anywayz
https://www.clublexus.com/forums/sho...5spd+swap+done
http://users.tpg.com.au/users/loats/...earboxes2.html
http://www.mkiv.com/techarticles/aut...wap/index.html

i realize the last link is a supra and an auto -> 6-spd, but the in-cabin mods and installing all the generic stuff is mostly the same

oh yeah, and whatever you decide to do let me know and ill come help you out if i can, always wanted to do it/see how hard it really is.