rebuilt an engine for my car and used a pair of twin 40 webers for the fuelling. but i had stripped the block down and after reading about your lots woes with the sump gaskets, i feared the worse for it leaking. and it don't and i didn't even use any sealant!!
the secret is to make sure all the surfaces are nice and clean and to torque the sump down in a diagonal sequence so the it compresses the gasket evenly. the only leak i had was coming from the dipstick tube, so i put on a new one and used vauxhall sealant instead of a gasket as they usually leak. all nice and tight now and not even a drop from the cam cover gasket.