Help with Head Gasket selection

No, you need some gap around the pistons and bores. The gasket and the bores are not guaranteed to be perfectly registered on the exact centers. Next step up in Cometic-land is 4.080", IIRC.

As for the rods, the copper colored ones may be reworks at the factory, or may be reman'd rods. If the latter especially, the rod lengths can be off, so that means to check EVERY piston height.

When checking with the dial indicator, and wanting to be precise, I will check all pistons to deck on top, bottom, front and back and lay it out on a drawing. Tedious, but you will know exactly how your deck sits. I will rock the pistons back and forth when checking the tops and bottoms and take the average.

.030" is getting a bit brave.. the local circle track guys occasionally stray as low as .025" and I just put together a 4 banger at .028" . But .035-.040" is safe. Cometic makes them in .005" increments in the range you are going to need. .005" is only going to be <0.1 points in CR.

Since you have new heads (straight and flat and smooth) I would think they will be fine. IIRC, Cometic has recently relaxed the RA requirements vs what they used to call for...

And yes, 6 cc is a decent number for the eyebrows plus a bit for the crevice down to the top ring. BTW, I am getting 10.1 with a .060" thick head gasket and the pistons .025" out of the block. DCR is right at 8... purty good for a 340!