I know Bob does not like the metal gaskets, and agree with him the fiber ones are nicer,
but I have used the metal gaskets many many times and never had a problem with them, I still trust them completly, they served VW well for many millions of engines.
The only time I pesonally saw a problem was on my brothers bug, he left a washer under the gasket!! .///
small air leak will cause the idle speed to float up and down, a large air leak will cause it to cut out at idle. If Jack did not find an air leak the first time, I'd be surprised if one is really there. With the washer under the gasket, the car would idle, but it would drift around. So you would need a bigger air leak than that or possibly a smaller one in a more detrimental place perhaps
It takes a LOT to knock a bug engine out of commision.
THis is a strange one.
Could your timing way off?
My only other thought is besides a possible leak ( shocked) is I had the same problem when I put my carb frommy 1600 engine on my new 1776 engine, I could not get it to idle, it was fine at high rpms. What I EVENTUALLY found was I had to back out the large adjusting screw waaay far to get it running......
sorry wish I had an answer for ya.
Good luck Marc.
Matt