early 273 pistons.

7cc's for the eyebrows? No way is it more than 12% of the combustion chamber volume: 1cc is about as big as a sugar cube! IIRC the entire 360 dish is a whopping 9.8cc's total. The eyebrow is only 1.350 wide, .500 tall and .095 deep (at deepest point). It (1) is about 40% of a 1.500 circle and the bottom is angled to a fillet so its not an easy thing to measure short of filling it with water and weighing the amount of water with the napkin piece you soaked it up with. My guess is less than 2cc's total. The pistons are still in the block so I cant get them level to fill and weigh water volume...OR fill eyebrows with clay, scrape top flush with piston crown, dig out clay and drop in a ml graduated burette with a known quantity of water (or mineral oil for a smaller miniscus) , see how far it rises with the clay bits in it and you have your volume in ml, which are the same as cc's.
As for the available head gasket, they are now 4.060-4.175 bore with maybe a .040 compressed volume for an additional 8.5cc's or more.