[Dave Boboltz]

From POWERSTROKE's question, regarding Chevrolet's use of the GMC designed BB V6 and its variants, including the 637 V8:

From an Encyclopedia of Chevrolet Trucks, not my data:

The first use of GMC designed BB engines in Chevrolet trucks was 1965. The engines were Toro-flow 478 engines in 60-80 series Conventionals, Low cab forwards, and steel tilt cabs.

IN 1966, there was a new short Low cab forward and it used 401-478 BB V6 gas engines. The biggest steel tilt cab introduced the toro-flow 637 along with the toro-flow 478.

In 1967, in addition to previous usages, 70/80 series series used 401/478 gas V6 and toro-flow 637.

1968 through 1970 basically unchanged.

1971 usages remained but GMC designed BB V6 engines were losing popularity to 366/427 Chevy V8 in Chevy trucks due to same power and less cost, along with reputation for better fuel economy (not my words).

1973 brought new medium duties and Chevy released 305/379 BB V6 gas. HD conventionals used 432/478 V6 gas engines.

1974 was the last year for any Chevrolet trucks to use the GMC BB V6 or its variants.

I do not see any use of the 637 V8 gas in any Chevrolet trucks. Since most of the Chevy HD trucks and all steel tilt cabs were built in the GMC plant in Pontiac, it is possible that a Chevy might have been built with a 637 engine on a SEO (Special Equipment Option).