1930's 40's 50's D4 dozer eng questions

This is my first day on this site as I have just ended up with a total of 2 complete and 3 partial machines. First the later engines of 4.5 bore vs. the early of 4.25 bore - do they use the same bottom end? The later engines have the decompression lever on the valve cover vs. on the 4 individaul cam follower plates. Also is there any call in this group for the older parts ? Thanks Jim

Gosh Jim, for a minute I thougth that was JR Ewing!! 😄
If you have the serial numbers of the D-4's that would nail it down as to what engine they had. (If they were original) The serial number would be something like 7U 1789 on a plate on the side of the engine and on the rear of the tractor.

No, bearings etc are different between the D4400 and D315 engines.

If you can keep them, I expect you can move parts from any of them. The most important thing is how close you are to the one who needs the parts (at least if they're very heavy)!