J heads upgrade

Go for the 2.02's. At minimum while he is installing those, have the bowls and everything cleaned up. Do some work on the shortside turn/pinch point. And a solid valve job. Even really basic work like this can get those heads to flow in the 230's. And can be easily done while he's in there. A good full port job will see 260-270. 230's is good for low-mid 400 horse on the right setup. 260+ is good for mid-high 400's. Maybe even 500 if you got it planned out right.

Make sure you get the heads flow tested after. See your curve. Where your flow starts to drop off. Then get a cam to suit. IE no point in getting a .650 lift cam when your heads tip over at .500. With the cam picked, you can pick your compression ratio. As you then can know your dynamic compression (DCR), which is much more important. With iron heads I'd say you want the 7.5-8 area. Depending on octane available in the area.

If you do have 10:1 compression. And keep your DCR up. And pick a cam with good duration/lift. Right exhaust, etc etc. I would not be surprised if you saw 450 out of it. As an example. A friend rebuilt a 360. Stock stroke. +.030 over. 10:1. solid roller cam (can't give away all their secrets) 2.02 valves and full port job on J heads. Made 430 horse, at the tire.