Reply to SJ:
Paul I just had a long conversation with the guy that ran our Cat machine shop dept. at the shop for about 35 yrs. & he did tell me that there was a couple sheets of service parts that Cat had with all the seat part numbers in it.Maybe at your dealer go back to the dept. that does the heads & I,ll bet the mechanic (machinist) can give you the part numbers you need as they work with them every day.
MM - The article you're looking for, is an insert into the Caterpillar Service magazine, Vol 22 - # 10, dated May 29, 1953 .. and the insert is headed "Valve Seat Specifications", and dated 15th March 1953.
This insert lists all the valve seat specs .. and insert P/No's, for all Cat engines from approximately 1928 to 1953.
The insert P/No's for the D315 engine, lists 2 head types .. Head P/No's .. 4F5508 and 3F9903 .. and the valve insert P/No's are .. 1H231 for inlet .. and 1H232 for exhaust.
The inlet and exhaust valve P/No's, will be available from the parts book for your particular tractor.