M motor refresh

[Levi - M Farmall Puller]

My M's motor doesnt have the as much compression as it did when i bought it 4 years ago, and im wanting to rebuild the motor, and since i pull with it too, i am also debating on adding a little more horsepower to it. I dont know much about the engine as is, only that it is the 248ci. What i would like to know is how hard would it be to rebuild it as the SM 264ci? And what all would it intise to do to complete this? Also is it out of the question to possibly to build the 450 281ci out of my straight M engine?
 

[TractormanNC]

I'd bet money that it is already 264. Hard to believe any Ms still have 3 7/8 pistons in them nowadays.

I'm interested in comments on your last question as I want to do this to my M.
 

[D Slater]

If you put 281 sleeves in it the block needs bored around 1/8 inch to do it. Sometimes you can run sleeveless and get the 4-1/8 bore. But you would need to measure and check for a regular piston fitting. Sometimes a special piston diameter is needed and the block may still need the bore trued up and honed to size. Pulling forum would probably have more answers.