A Powerglide for a car 235 would be a bolt-on installation, assuming you can find the right flywheel (flex plate) and the adapter ring that bolts onto the block. Powerglides have two speeds- - - -"Too low and too high!" The only other bolt-on would be the 4 speed dual range Hydramatic- - - -scarce, expensive, and difficult to adjust the throttle linkage for proper shifting. There are vendors selling adapter plates for transmissions like the Turbo 350 and 400, and the 700R4, etc. The quality of those items varies from mediocre to excellent (Translation: E$$$$PENSIVE!)

Putting a "Belly Button" V8 in place of a good-running 261 is a huge leap in the wrong direction.
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!