Carb Gasket

I would expect to see a tufnol (or similar) 1/8" thick gasket/heat barrier between the carb and the head. Your disintegtating gasket shouldn't have disintegrated though. Most just have a paper carb gasket.

You need to be very careful "tightening" the carb as too much will result in a bowed flange. Certainly enough to split a tufnol spacer is too much!

I always use the single spring type washer and tighten till it just flattens. This will not come loose, is tight enough to stop leaks but not enought to cause distortion.

There would have to be quite a lot of heat to cook a paper gasket to the point where it turns to ash. Perhaps your gasket was poorly made from inferior material. A bit like cheap cylinder head gaskets that can be found on the market at the moment.

You do need the Tufnol washer to prevent the carb getting too warm and vapourising off the fuel. On my engines I add a thin smear of Silicone RTV goo, on each face, to help seal the joints. This allows very close contact between the respective parts and also fills any dings, dents and bent bits.