Issue with stalling when in gear

Already rebuilt the carb.
I'd start with that as a possibility.
Which carb?
I determined it was not the transmission after having it rebuilt.
Wait, you suspect the transmission was causing this same problem? I don't think any of us would have guessed that from you first post.
It sounds like the engine lacks power at idle and off idle.
My suggestion would have been to start with checking fuel level, idle mix and timing.

Maybe I should consider putting HEI on it.
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When there is problem, its best to trouble shoot it. Keep projects seperate.
Gonna start with the points, new intake gasket.
OK. I could understand points, but why intake gasket? That's a major project. What clue is there that it related to the intake gasket?
As far as points go, the beauty of them is you can see the wear. On the other hand the condensor, especially new ones are a crap-shoot.

If you want to look at anything, I'd suggest spark plugs and fuel level. Also make sure pump shot is working.
Then go to initial timing. Set it with the vacuum advance plugged, and to the rpm in the spec. Then adjust the idle fuel mix. Then check rpm and timing again, and if its different, adjust the rpm, adjust timing if needed and then fuel mix.