Hi Roy,
I always fit a solid insulating spacer (tufnol) next to the head then a gasket, the skislope and the carb
If the carb body is in good condition the O ring should be enough
A smear of sealer either side of the insulating spacer is enough
Any "soft" materials in the assembly makes carb body distortion more likely
I hate those thick soft so called insulating gaskets, they cause all kinds of bother
John