My advice is similar to previous postings; look for a list 3310 with the secondary metering block. Adding the block is straightforward if you can't locate one that already has it.

Spend a few minutes looking the carb over thoroughly before buying. I've seen base plates cracked, shaft's wobbling in the base plate, accelerator pump cover screws stripped out and junior high racer mods made to them which generally render them useless for a street car. A favorite seemed to be removing the choke assembly and sometimes milling down the air horn.

Rebuild kits are inexpensive and readily available. Go with the non stick gaskets though. Generally you shouldn't need to increase the accelerator pump. Stay with the vacuum secondary setup. Linkage and brackets available on line. I'm not an expert by any means but have been running these for years. Have only had one that would not work well and turned out to have a crack in the base plate I'd missed. Being up North ours have to be put away for winter. I've always used sea foam in the gas tank before storing and haven't had problems. No other fuel related issues I've run into. Lots of good books available on line if you're so motivated.

Many years ago I had an Offy 2 4 barrel setup with AFB's on my drag car and ran it like that for at least 4 years. On a whim I changed out the intake and put a stock 3310 on the car and first pass out it went 2 tenths of a second quicker than it ever had. Did I feel stupid.