My truck is a 1/2 ton, and the valve cover says Chevrolet on it, so sounds like the original 248 was replaced. The serial number has no numbers that indicated the engine size.
Too bad I guess. It is definitely powerful, just really low geared.
This things has been more reliable than my 92 Acura Legend, has never failed to start in 3 years. Hate to start tearing it apart.