In the "Power Manual" doesn't list that casting number. It does list "3921968" as a 1966-70 Car 230, and as a 1962-79 Truck 250. If that's the original engine then it should be a 250. Hope this helps. John
'68 C-10 - 250 with Edelbrock 600cfm 4 barrel, Offy intake, Hedman headers and true duals, HEI, MSD 6A box, relocated gas tank
Soon to have: T-5 tranny
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