I am not going to be much help here but I will say that make sure you have the Cat Ten size piston starting engine because the later starting engines have a larger bore. Starting engines seam to have moved around a bit over the years of the life of a tractor. My paper version of the NPR shows no change in part number, if you ask Cat the number would be either 0T0245 or 0T0246. That also being said, find someone that is selling rings for a Cat Ten and get a half set from them. Same rings.

The problem I have right now is I do not have a Diesel 35 or 40 parts book here so most of this is going off of memory. The rod is a different part number than the 10 because of the difference between splash lube used on the starting engine and the pressure system used on the Ten. I would guess that the length of the rod is also different. The small end bushing is the same along with the big end shims and rod bolts. The valves, valve guides, springs, locks, retainers, lifters and adjusting screw and lock, the lifter guide are all the same as the Ten. The valve spring cover, gasket and nut assembly are the same as the Ten, but the nut changed from cast iron to die cast somewhere along the way. Camshaft end plug the same as the Ten

Measure the bore of the engine and that'll tell you if it's oversized.
A standard Ten bore is: 3.375"

Ring gap should be .012" to .020" for comp and oil rings. Cast iron pistons having a skirt clearance of more than .012" to .005" should be replaced. New cast iron piston in a reconditioned cylinder bore should have a skirt clearance .003" to .005" An aluminum piston should have a skirt clearance of .010" to .012"

Later starting engines have 3 5/8" bore, standard piston is part #1C0001, .020" over is 1C2241, .040" over is 1C2242. Semi finished piston is1B1657. Standard comp rings are 6B2850 and oil rings are 6B2298. .010" over is 2B6066 comp ring and 2B5156 oil ring. Standard con rod is 2A2367 and .020" under is 3B8278
Let me know if you need specs for the 3 3/8" bore engine.