Wow, sounds like you got yourself a project!
I actually had a Sears rebuilt engine put in my 1949 Dodge around 1975. It's still there, and I have the tag that came on my motor.
btw, Sears didn't do the rebuilds themselves, they just bought remanufactured engines from whoever was conveniently located.
The tag on that motor would have a number code indicating engine type, probably a code for amount of overbore to the cylinders, and undersize for the crankshaft journals.
If it's been sitting since 1971, especially outside, it's probably siezed. You'd be lucky to get away without doing a complete rebuild on it.
The fact is though, once you get the pistons out of the way to do a rebore (assuming it's siezed) you'll be half way to a complete rebuild anyway.
There was performance stuff made for them.
Here's some on my Dodge motor, you can get all the same stuff for yours if you look hard enough
I don't know if he still has it since I passed the same info on to another poster here, but the guy who put the hotrod stuff in my Dodge, has (or had?) a nice Edmunds aluminum high compression head for the Chrysler motor. Call Jerry at 541-683-5998.
For NOS rebuild parts, call Doug at 541-726-5601.
Good luck.
