Cylinders must be bored if you are going to use oversize rings.  According to what you said, it doesn’t need boring/oversize.  There is something you aren’t telling us.  NO compression???  Even worn-out rings will produce some compression.

Edit:  Replacement water pump kits have small impellers.

• This reply was modified 1 year, 4 months ago by frankr.

check for bad head gasket first.

Well 15 psi certainly is low or “none”.  65 is borderline.  Were the rings stuck or something?

If the motor has overheated, you should see signs of overheating such as discolored paint on the cylinder head, and relatively loose cylinder head bolts. A bad overheat will produce scored pistons and brittle heat weakened rings. It doesn’t sound like this motor experienced a bad overheat. If the motor hasn’t overheated badly, then the rings may be salvageable.

At this point, it may be prudent to take a very close look at the cylinder head. Inspect the head for any tiny cracks, or imperfections. If it passes inspection, resurface the mating surface by lapping it on a plate of glass, or a large, polished floor tile. While you’re at it, inspect the mating surface of the block also. The block can also be lapped if it has gouges or is not flat.

I believe the standard rings for that motor were used for many years going back to the 1940’s, and into the 1960’s. There are older part numbers that may help with your search. Try PN 378432 or 041333.

• This reply was modified 1 year, 4 months ago by aquasonic.
• This reply was modified 1 year, 4 months ago by aquasonic.

“There is an ever so slight wobble to it that is not excessive that could indicate that the head is out of tolerance.”

This may be the problem, or part of the problem. After lapping, the cylinder head should sit perfectly flat on a large, polished tile or plate of glass.