Strip the entire running gear out, bellhousing, transmission, torque tube, and rear end, and replace it with open driveline components. You will also need to change the crossmember under the bellhousing to accommodate the one that fits the V8 - - - the shape and position of the motor mounts are different. You will have major clearance problems between the steering column and the driver's side exhaust manifold.

The 55 year 265 engine is unique to that year- - - - -it has a bypass type oil filter mounted at the front of the intake manifold instead of the full flow filter built into the engine block at the left rear of the 56-up engines. Someone who is doing a period-correct restoration of a 55 model V8 car or truck will probably pay enough for your engine to buy a newer, more commonly available engine, with enough cash left over to help buy other bits and pieces you'll need for the V8 swap.
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!