The W58 in the NA Supra's don't work well as the input shaft is too short for any kind of an adapter between a stock bell and the trans, and it has a different bolt pattern than the R154 so the Dakota AX15 bell wont work. It's a good trans, and has been know to hold 400 hp or so, but I don't think it is much stronger than a T5, and the hassle of making one fit would make it less than ideal to say the least.
For my slant project, I would have prefered the W58, but couldn't find a way to make it work without some high tech cnc equipment. So I started down the R154 trail...