Man, trust me, I'm informed
If you've got a tranny from a Jspec 90 GT-S, it means that it came off a JDM 3SGE (All Japanese GT-S in 1990 came with that engine). The 2nd 3SGE is roughly 170hp stock NA, which means that the tranny will be a little bit stronger that what I've got right now, but it was never built to handle excess of 260 lb/ft of torque, that's a fact. I've spoken lot's of people in the US that have done 3SGTE swap on 5th gen celicas and used their stock trannies. Some have held but more than one blew to pieces.
To say that your tranny is "unbreakable" is rediculous, there's not such thing. Maybe it would hold and maybe I'll end up taking that risk. I never questioned whether or not you had a good transmission, I'm sure you do and if I run into anyone looking for one I'll let you know.
Seeya