What camshaft should I use?

Not one that works. The carb on there is a 1920-6156 which had a bad metering block. It would fall flat on its face and stumble. I tried to use the correct 1920-4354 and it turned out to have a bad air horn, so I took the two and made one good carburetor and the car runs without a stumble.

Leak down test the motor, then we can give you better advice.