Actually the Supra MKIV tranny code isn't the same as the SC400. The Supra is A340E and the SC400 is A341E. However, the hi-performance internal parts are the same and that's what I know. I don't know about OEM internal parts, though.
A trick is to pretend that you have a SC400 so you can check for the part number at a Lexus dealer. You have to come up to the part guy and ask for the diagram. The diagram will show you where it is and also the part number as well.
Another tip is to check on Ebay for the images of both trannies. If the both's exteriors are the same, then more likely they use the same mounts.