Good info; all that helps. Find out the pistons that you have so we can get a complete idea of the guts in the engine. If it was a top end change out on a stock engine, or if the bottom end was rebuilt to stock specs, then just let us know that.
I am suspecting that with the heads, assuming they are the Small Block Edelbrock clones, then the pistons in your engine are not stock replacements. And I assume you mean 1.60" on the exhaust valve, not 1.9"....
Head gasket brand and part number would be good to know too.