Please recommend tune-up specs

Hi,
225 offenhauser 4bbl intake, adapted 2 bbl Rochester (newly reman+ removed auto choke convert to manual), auto trans, headers,3.73 gears, Dana 20, manual choke, Delco points distributer, accel supercoil. no AC, or PS but I have an operating plow pump. Runs rich, boggs a little under small load, "coughs" once in a while under heavy pushing( backfire carb ??) I have to crank and pump a lot to get started when cold.
I have the timing at 5 deg before and dwell at 30 like it says. The mixture I leaned out the best I could to highest RPM.

Suggestions please,
Josh