Wowwwww
Thats an aweful lot to know for a newby Motobunny...
This a very good point, not a LOT, but some few 2 and 3 horse Tecumsehs were a cast iron bore.. The engine I am running on the Litening Trike rite now is exactly identical to the one you posted.. This orange engine of mine, is a cast iron bore, 2.5 horse... :thumbsup:
Mines ugly as hell and was missing some stuff, non running left for dead in the barn, but they were (born) the same.. I'm willing to bet yours was born with a cast iron bore too..
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And yes, 70's probably like 1977 for an exact guesstamate, give or take a couple years..