The 637 was the largest V8 gas motor ever put into production by GM. It's HP was rated at 250 @ 2800 rpm. Be prepared for 4-5 mpg. I had a 1970 Chevy T-80 Tilt Cab Telephone Pole Winch Truck with the 478 V6 and it got about 6.5 mpg. My 1970 T-60 Fire Engine has a 427 V8 and it's no better on the gas mileage.
Good luck, looks neat!
Mike B
