Where to get 273 Head Gaskets?

I've run the 4.000 fel-pro .039 for decades and cannot tell a difference. I've run them on 273's, all Commando's, with original heads up to pocket ported and cc"d 1.88 intake "J" heads. They've all run great! I have ordered 2 sets of the 3.625 diameter fel-pro's above from Summit Racing, since finding of their existance here. I believe a small loss of compression will make almost no difference, but I'm an Engineer. I also mill head and intake sides of the heads to get the best surfaces to seal to. That's my 2 cents.