There is no good reason for the average person to set timing by ear. It may work, but why not have the peace of mind that your timing is set correct? Going by ear, you don't even know beyond a reasonable doubt that you're in the ball park. Even dial back timing lights are cheap enough on that auction site.

Secondly, after you've got the timing confirmed, check to make sure your plug wires are routed correctly. Supposedly there's two wires on BB mopars that are easy to mix up but will still run. Never happened to me, but I thought I'd throw it out there. How new are your plugs/wires/rotor/cap?

Next after you're sure it's not an ignition timing problem, try manually disconnecting the secondaries on the carb. If it still runs poor to 3500rpm, then I suspect you can have a jetting problem there.

Another thing, you say you have a mild cam in there, what's the specs on it? I have to ask because a 73 400 will have low CR pistons in it. Also, was the cam degreed at all during installation or did you just line up the dots?