I thought you could just swap the bell housing off a R150 and a R151 and you were good to go?  I was under the impression that the only differences were: 1st gear is lower on a 151, tail housing is different (for a gear drive case, but you can swap them back and fourth), and the bell housing was different (got the 3.0 vs the 22re, but again interchange able).

If I were you I would see if the bell housings swap. I seem to remember that the Supras use the same tranny (I think its called a R154) and guys who do the supra swaps just get the bell housing from the same car and hook it to a R150 or R151. It would have been more than a year ago that I read this so confirm it before you go out and try it!! (they may of had to do a input shaft swap as well...

Also the R150 and 151 are the same as a jeep AX-15 just with different housing, and input and output shafts. It is conceivable to put the back half of a R151 on the back of a AX-15 (including output shaft) so that a gear drive yota case will bolt to it (I have never seen anywhere where this has been done, but in theory it should work).

PZ