1976 GMC K15 7.4L V8 VIN: S CARB 4BBL Naturally Aspirated GAS. 1976 GMC K15 7.4L V8 VIN: Y CARB 4BBL Naturally Aspirated GAS. 1977-1978 GMC K15 6.6L V8 VIN: R CARB 4BBL Naturally Aspirated GAS. 1976 GMC K15 6.6L V8 VIN: U CARB 4BBL Naturally Aspirated GAS.
