A 54-62 235 or 261 is almost a bolt-in fit with only a few minor changes needed. 54 and early 55 engines even have the water pump in a similar location as a 216, but later model engines can use a pump relocation plate sold by a longtime member of this forum. Virtually everything else is a bolt-in swap, and the 261 in particular makes a huge difference in performance.
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!