There is a whole school of Aisan Warner transmissions that share the same trans to bellhousing bolt pattern, meaning any of these will bolt up to the Dodge Dakota 3.9l / 5.2l AX15 bellhousing.
The R154 (freshly built will handle 500hp. The Turbo Toyo Supras are kind of a cult car, and they are commonly built out to 800hp and more. I understand that the MA5 from the Chevy Colorado / GMC Canyon pickup trucks (also used in Pontiac Solstice and Saturn Sky) has latest and greatest tech and upgrades in the syncros, which is a huge aid in trans being able to live with power. There are differences in input shaft length and spline count that will need to be addressed, but there are many good starting points.
Been searching my computer, here are a few links that can be of use;
