Hi Team,
scans are a list of Instruction Books ---Operator's Instruction Books and Servicemen's Reference Books--- available up to that time, Dated :- October 15 1949, Form No 8938-2.
Servicemen's Reference Books are on page/scan #4

If you require an Operation or Service Book for an earlier S/No machine than is listed here then it likely was never printed by Cat.

ie,
D7, 7M and 3T were the first D7 Servicemen's Reference Book literature printed up to this date--if you have say for example a 9G RD7 then there appears to be no Servicemen's Reference Book for that S/No range machine.
Cheers,
Eddie B.