Don't assume anything. The MKIV and Lexus models all used a smaller extension housing which had an external shifter carrier bracket attached to put the shifter even further back... Like the item in the first picture here:
http://www.vadriven.com/forums/engin...?t-322966.html
This assembly would not work for the MKII, MKIII, Cressida, nor any of the trucks that I've seen.
I've given you a list of vehicles which come up when looking for specifically the extension housing in the EPC. I don't know what differences there may be but as they are all listed I suspect they may all be compatible to some degree. Check the EPC and see what you can find.
Keep in mind that there may still be other differences such as the configuration of the output shaft (length, diameter, spline count). If you can get the shifter in the right place any issue with the output shaft can be deal with by a good drive shaft shop.
Personally, I'd look harder for someone who's done a GTE/R154 swap or someone who's parting out in your area or neighboring states.
Check with these folks
http://greenville.craigslist.org/pts/2945380106.html
http://greenville.craigslist.org/pts/2909596039.html
R154 but call and see if they have a W58
http://columbia.craigslist.org/pts/2864069904.html
Check CL for other close by states. Check the parts for sale section over on SupraMania.com too.