Shaved heads and head gasket thickness.

Hello all. I've come across some "J".heads from a 1970's C/Gas car. They've been shaved enough to consider them closed chamber heads now. I have KB pistons with small domes that protude a bee's dick above the deck. With a second hand FelPro head gasket and some plasticine on the piston I can turn it over but there's only a cigarette paper thickness clearance. Felpro suggest their gaskets are .039" thick.
What gaskets have others used with severely shaved heads? Who makes a thicker head gasket? Can you help me with a part number?
Cheers