Understood on the cylinder checking procedure as you have it. It would indeed be good to have the numbers with the stock cam still in there. Is this a cranking compression test or a leak-down test? I thought the engine was out and torn down...?
I would assume that the Felpro set has the 8553PT head gaskets; those are gonna be .020-.030" thicker than the stock ones, which is another 3.3 to 5 cc's of chamber volume...ow! The thinnest that you can get inexpensively for higher CR is the Mr Gasket 1221G's at .028" thick.
Ah OK, the cam is there.... yes I absolutely would advance it. I'd set the ICL at 104 or 102. 4 degrees advance makes a very noticeable improvement in low RPM torque and throttle response. I can't see from the Summit page what the ground-in advance is (where the advance would be with the cam installed dot-to-dot) but I'd guess it is 108. So another 4 degrees would get you to 104 (if 108 is indeed the cam's ground-in advance).
I'd advise doing the cam timing properly; you need to borrow a dial indicator, or figure up a way to have a definite stop on the cam at .050" intake lifter lift. You can get a free printable degree wheel here:
The Machinery Cleanery Universal Timing Disc, Degree Wheel, Downloadable - Goniometro per Messa in Fase dei Motori a 4 Tempi -
I use that and glue it to poster board and VERY carefully cut out the center hole to maintain accuracy.
And you are right on one thing.... at least you don't have the older large chamber 318 heads!
