I am working on a Kohler M-20. It is in need of a rebuild. I have the Kohler TP-2233-C parts manual. I noticed this manual covers both the M-18 & M-20 engines. This got me wondering about the Crankcase Core. Is the crankcase (halves) the same for both horsepowers ?? The variants come from the crank, jugs, and external parts options with the Aluminum Castings being the same? According to the TP-2233-C, it says to refer to TP-2253-D Selection Guide and leaves it at that. I have the TP-2253-C, but not the "D" version. Thus, is my assumption correct or not. Looking for any and all advise.