I've got an 81 with the lean burn Holley 1945 carb, it's got new manifold gaskets, and will start and idle, but as soon as it gets warmed up, it wants to die and not restart. I was told to convert to a Holley 1920 from the early 70's and it would solve the problem. Any help?

Do you still have the lean burn ‘computer’ controlling the ignition timing?
If so those are unreliable and for the most part not repairable, so if you
have the lean burn system active, that is likely the source of the problem.
To eliminate the lean burn, a carb like a basic 1920 and an electronic vacuum
advance distributor with a HEI ignition would be the solution.
You could also use an old slant six points distributor.
It is possible the 1945 carb would still work for you if it has no wires going to it.
And the lean burn was only controlling ignition timing and had no control over fuel.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

It still has the lean burn system on it. I found a vacuum line split and plugged the vacuum line that ran to the canisters after I tried putting a line back on, it stalled the carb... could this be the issue? If I don't have to put a almost $300 carb on, I'd prefer not to... but I am afraid the lean burn will cause more issues for the carb.

Does your existing 1945 carb have electrical wires going to the fuel bowl or anywhere else on the carb?

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Yep....

Yes, you will need a different carb.
A 1920 or a 1945 without wires so you
can ditch the lean burn.
I got rid of all my one bbls some time ago
or I would make you a deal on one.
Try putting a posting up in the parts wanted,
Look on e bay, bet you can find a solution for
a lot less than 200.00
The carb may need gone through and rebuilt but
one bbls are not bad to work on.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Already have a rebuilt 1920, I'll install it today.

I used a Holley 1945 once I yanked the Lean Bum off mine (without wires) and discovered quickly that they were prone to wobbling out the throttle shaft hole, which produces a vacuum leak. But the 1920 also has its known troubles in that area, plus a metering block that cannot be serviced once it's clogged. I ditched mine after a few hundred miles because it started sputtering. If your 1920 craps out, if you can find a BBS snatch it up.

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If it was easy, everybody would be doing it.