Rebuild or replace?

A motor with bad compression rings will run hot. I would say that 273 is destined for the metal pile unless your looking to keep a numbers matching motor. They are not worth the effort. Just getting a good torque converter for that crank with the smaller snout will be costly. Look for a 71-74 318 with the trans attached. They usually have a decent converter from the factory. Your early timing cover with balancer will work for the correct water pump for the car. The only thing you will have to change is add the back-up light wires to the trans switch due to the later valve body. You will be way ahead of the game with a 318. 360 you will be hunting install parts that are not cheap. There will be a list of things just to install it.