The two big concerns will be the bellhousing and the front motor mounts. A 1955-up V-8 bellhousing will bolt up to the 250 block and the original transmission, but the bellhousing crossmember will also need to be changed due to different angles on the mounting surfaces. Up front, some side-mount brackets will need to be installed to match the engine mount pads. The rest of the swap is fairly simple.
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!