super"c" with "c" engine???

[dw]

I have a super c which maches the serial number, and has the original motor in it, but when i removed the head i found it was a 3in. bore not a 3-1/8. The 3in bore is the motor of a "c", not a super. The tractor is a 1951. WHAT IS GOING ON????????? Everything else on the tractor matches up to a super c. Please help me>>

[Eugene]

The engine casting # for the C is 251069 and the Super C is 354898. both located on the right side behind oil filter.

My guess. Engine replaced at some time in the past.

Eugene