Hi Coal - I did almost the same thing with my '64 C20. It was originally a 292 3 speed on the column. The motor was really tired so when we did the rebuild we used "propane" pistons, added a very mild cam, Clifford 4 bl intake and Hedman headers. (He's "Otis" in the Gallery.) We also changed the 3 speed to a 5 speed and it works great as a driver. We do tow a trailer with our '56 Chevy on it and it does OK - it works hard on hills or fighting strong winds. When we put the engine together I had a 465 cfm Holley carb that I figured would be pretty close to what it would need so thats what we ran it with. It ran OK but seemed a little weak at lower rpm and didn't seem to have "crisp" throttle response. The plugs looked really white but I was thinking maybe they were a heat range too hot. On a whim I tried a different carb. I had a box stock Edlebrock 600 which I figured would be too much for it but thought I'd see what it would do. I was amazed. It ran MUCH better - throttle response was better it would pull from low rpm better and the plugs were tan. I know that on paper that is way too big a carb for that engine - I also know the engine runs way better than it did with the smaller carb and the fuel mileage is the same. For what it's worth...

1964 Chevrolet C-20 Fleetside, Otis
1950 Chevy 1/2-Ton, Kirby
1950 Chevy 1/2-Ton Shortbed, Walter