Carb for 273 commando

I have a 600cfm edlebrock on a standard 273 I would not recommend it, had to jet it down a lot. I think a 500cfm would run much better on my engine. But I have not found one at the swap meet that looks like it would be usable for my self imposed $100 max purchase price.

Anybody know where to find and what part number for a rebuild kit for a stock 66 formula s carb. Looks like a 4121S carter carb???