Master cyl install

I have a 66 barracuda with power brakes. The rebuilt master cyl has a tab and screw holding the piston in on the mating surface to the booster. The original thick gasket for the master cyl. Is not usable, and the rebuilt did not come with a gasket. Question 1, does the tab holding the piston in remain on the master cyl. When you install it on the booster? It seems to me the master cyl. Would not sit flush on the booster even with a thick gasket. Question 2, anyone know where I can buy the thick oem gasket for the master cyl? Thanks
I'm interested in your findings, I will need one as well.