Since you're dealing with a small block (10 head bolts), I'd recommend leaving the decks near stock, but have it decked to bring it to 9.6". Most will be within a few thousands of that spec, and doing so will not affect any other engine component.
I'm in the process of building a similar engine and the first thing I noticed was the pistons were .380 down the cylinder, which means it would have been lucky to make 7.0-1 compression and, yes, it was a DOG... The compression height on these pistons was a (shameful) 1.440, and without a piston upgrade, it'll be very difficult to make any decent power with it...and there's simply not enough material in the decks to get it anywhere near a zero deck height. It's getting new KB pistons...
For your car:
Optimal deck height will be 9.6", and you should have your machinist "true up" the decks to this dimension.
Half your stroke comes out to 1.655
Your rod length (ctr to ctr) is 6.125
9.6 - (1.655 + 6.125) gives you distance from wrist pin c/l to the top of the piston at TDC to attain zero deck.
9.6 minus 7.780 leaves you with ~ 1.820 for a compression height that will bring you to Zero deck - without factoring in a head gasket.
Zero deck means the flat surface of the piston is level/even with the blocks deck when at TDC, and it's preferred because it maximizes a concept called "quench". The more quench the better, and keeping your pistons near zero deck height will maximize quench. Large quench aids flame propagation and results in a more intense combustion cycle when coming off TDC.
Since you're looking for ~10-1 compression (same as the original 340's) you could run a standard Fel Pro gasket which, IIRC, is around .050-.055 thick, should put you in the ball park. Torque the stock head bolts using motor oil with the stock fasteners.
I hope this helps, but you really need to measure how far down in the block your current pistons reside. That will go a long way toward determining your path/expenses going forward. Let us know how it works out.
Southernman
