Using stock replacement pistons has most likely been the 'bad' decision during the earlier build-up I would think.
You probably ended up with less compression an above that the, I suppose, composite headgasket used lost you some more compression. With stock pistons and open chamber 906-heads you won't have any pistonquench either.
You could try to advance the cam to see if you can build some more cylinder pressure at low rpm, but don't expect much from that.

i agree with Randy, but in the end, you 'know' you rather want that stroker motor under the hood

I'm running a 500" in my heavy 1960 NewYorker.
Stock Edelbrock heads with shorty headers into a 2.5" dual exhaust. It gets 17mpg with the 3.23 gears in the back, but still roasts the 275/60-tires through first and second gear. With a stroker you don't really need anymore gear in a street car.
Oh, my heap runs 8.6 on the 1/8 mile.