Are you saying that the base of the carburetor is warped? If that is the case it seems that you could flatten it with a large flat mill file. Be very careful with the chips, it would be best to remove the baseplate from the carb for this milling job so that you don't risk getting any chips or filings in the carb.

Also, you could get some very heavy gasket material and make a thick gasket that could seal it up. Are you SURE the phenolic spacer is not cracked?

Good luck,