So Hypothetically.....(318 swap)

1. Stock 273 mounts will work fine since the slants and the V8s used the same K member until '67.

2. A slant transmission will not bolt to a V8 because the block pattern is different. You will need a V8 transmission. Fortunately, the powertrain length is the same so you will not have to cut the driveshaft and the transmission mount is in the same place. They even use the same mount.

3. You will need a kickdown of some sort (stock or cable kit), a cable throttle pedal assembly (your slant should have a rod setup), a V8 radiator, a V8 center link for the steering, a 90 degree or remote oil filter adapter, and some sort of exhaust. Stock A body V8 manifolds work fine for most uses. You have to be a real masochist to want headers on an early A and clearance is an issue since the engine bay is the narrowest of all A bodies.

Not required but a nice touch are beefier torsion bars and better brakes than the stock 9 inchers. You may also want to check into a rear axle upgrade since the stock 7 1/4" won't last very long behind a V8. Hope this helps and good luck with the swap. If you have any more questions, sing out.