[Awtoman]

Gm used two rear wheel drive bolt patterns at the rear of the block for transmission mounting. Buick, Olds, and Pontiac used one style, and Chevy had their own. You need a 200R4 for the Buick engine. 700R4 has a Chevy bolt pattern, although it's possible someone makes an adapter plate. Either trans can be built strongly enough. You're not making a lot of power, but a 1/2 ton truck is heavy, and when those trannys first came out they were a little weak.

Tom