Sounds like a vacuum leak to me. Its the first think I'd check. Especially with a rebuilt carb. Recheck the idle screw, seal from carb/manifold, vacuum line, or get yourself some starter fluid. You'll find it quick.
If not that, see if the mix is lean with a vacuum gauge.

Sorry if it sounds elementary, but lets try the "free" stuff first so we don't just throw parts at it!
I have a 65, and sometimes the idle is hard to pin down.

 

 

When in park, are you able to floor it without stalling the engine, or pops from the exhaust?

 

In park i can rev it all i want. I actually found the pcv valve was a little loose going into the valve cover so i wrapped a piece of tape around the tip and it snugged up nicely, so nice that it started up went in gear and i drove it around the block for the first time in about a year. brought it home checked the tire pressure and was going to take it for another spin and it stalled again when i put it in drive.