Bottom end info?

Low 12s with a stick and a good driver will need to make about 425 hp at the crank and the right gears. The J or X heads could do this easy. If it were me, I'd have the Js flowed to see if they are ported well, or just look good. A little bowl cleanup, and gasket matching, and you'll get 425 from them with the right cam. You could also just sell the Js, and use teh $$ for the Xs. They'll need a little I'm sure. They always do. Dont skimp on the valve work. You'll make more power with a great valve job and ok port work, than good porting and low end valve jobs. If you want a pump gas engine, you'll need to keep the dynamic compression below 9.5:1. That depends on both your static ratio, and the closing event of the intake valve of any cam you plan to use. You can build a higher static ratio (like 10.8-11:1) and run a modern cam with iron heads and be fine on pump premium. I'd go like 11:1, with a cam like this Crane (hydraulic, runs strong between 3K and 6K, peak hp should be around 6300 depending on heads, and will be "softer" on the tires when you side step it..lol).
http://cranecams.com/?show=browsePa...-360 C.I.&partNumber=690221&partType=camshaft

For the rest, either an M1 single plane matched, or an Air Gap RPM matched will do fine. I'd lean towards the air gap.