Welcome to CHR!

I have to concur with most of the above. If this vehicle is intended to see street use, you have too much carburetor, probably too much compression and in all likelihood too much cam. More information would be helpful for a diagnosis and as Jack mentioned – the entire package needs to function together.

Do you have the casting numbers for the heads? Not trying to be negative, but not all camel humps were created equal. Did you assemble? How did you come up with 10.5:1? Are you certain they're 2.02 valves? Did you have the heads surfaced? What was the final volume of the combustion chambers? Was the block decked? If so, what was your final measurement (looking for a number somewhere between 9.025 and 9.000).

If it were mine, I’d pull the heads and measure the deck clearance to determine if I could get the C/R down below 10:1 with a thicker head gasket. I’d then e-bay the Victor Jr and go with a Performer RPM and a 600CFM Edelbrock 1406 with the electric choke. You may need to lean down one size on the initial out-of-the-box jets and metering rods.

Assuming the valves are correctly adjusted, the backfiring is probably caused by 16 degrees of initial timing – much too high as is attested to by the fire happening while your intake valve is still slightly open, but with the cam you have it may not idle much less than 12 degrees. Ideally, the initial timing should be 8-10 degrees and 34 degrees all in (around 2000-2200 RPM). If you cannot get to this point, the cam may be too big.

6-10 inches of vacuum is unacceptable (in my opinion) for a street driven car. 20 inches of vacuum is a better number, 18 is about as low as I’d go on a street car with power brakes and below 18 is just scary for overall braking a 3800 pound car in a hurry.

My two cents - keep us in the loop and once again, welcome to CHR!
Glenn