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I think if your pushing over 160+ cranking cylinder pressure you may be pushing the limits for pump fuel on an older iron headed engine?

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This is a fairly acurate statement. And people who insist on useing old outdated openchamber iron heads will always be saddled with this. Why for the differance in price would any one use regular old J heads X heads or something when you can use a magnum style head for only a tad more. Same with pistons. Why leave 50-75 lbs of tq on the table since you need heads and pistons any how? And a good combo of KB 107 pistons and magnum heads can easily add that over stock low comp 360 pistons and open chamber heads. Plus you will get better miledge so why saddle him with old information? My first engine that was anything not totally stock was a 360 KB 107 combo with 302 heads that I heavily ported lightly milled and ran in my 68 dart. The only problem I had with detonation was the fact I left very sharp corners on the pointy thing in the middle of the chamber, I had to pull the head back off grind that thing down and it was fine. The magnum don't have that thing and has a way better chamber so he should be more than safe.

Also someone mentioned putting a carb intake on a JY 5.9 that is a good idea as far as simplicity goes. It will make more power than the 300 hp crate motor because the stock cams are actually bigger than the 300 hp cam. Also of interest is how those 300 crate motors always seem to make more than 300hp even with 318 manifolds. People never give the magnum heads the credit they are really due.