Its hard to get a tight quench with open chambered mopar heads. If you measure them you may find the chambers are not as equal as you might think both volume and height. Octane needs of the engine have more to do with dynamic compression than static compression. I use an engine program to decide what kind of fuel the engine will need. Performance trends, it calculates cranking compression, advance curve, and lets you try different octane fuels. It also calculates a ton of other stuff. Results on a real dyno are close if you take the time to put good numbers in the program. And it costs about what a good 1/2 ratchet costs.