There's an adapter kit available to swap a Turbo 350 or 700R4 into your truck, and bolt it up to the original stovebolt engine. It does require switching to an open driveline, however. I believe a center chunk from a later model pickup will bolt into your existing housing, but you'll need to set the pinion angle correctly and weld the pivots at the rear springs to make that conversion work.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!