Sassygrass,
I have some experience with the J's. I ran them on my 70 Swinger. They had 2.02 and 1.60's in them and I hand ported them myself which is the first time I ever ported heads. I had them flowed and at 28 inches they flowed 255cfm on the intake and 190 cfm exhaust. These heads were on my pump gas 360 and it made 490hp at 6300 and 460tq at 5200. My car would boil my 275dr at easy from a roll and would run 11.60's at 115 mph in a 3400 pound car. I ran a torker 340 single plane with a 750dp holley. I hope this helps.