Hypothetical 360 magnum build

> any cam with a later-closing intake valve will lose cylinder pressure.
> any pistons with a shorter pin-height will reduce cylinder pressure.
>Giving up cylinder pressure is never a good thing, especially for fuel-economy, in a heavy vehicle.
> those 3.91s x .69od= 2.70 final drive, just about right for the factory cam. The tall tires will make that feel yet smaller.
> the octane requirement changes as a function of effective cylinder-pressure, which changes with load/rpm/and chamber temperature. You don't get to decide what octane to run in an unknown combination of parts, unless: 1) you have empirical supporting evidence from a prior similar build, or 2) the combination is EFI with a knock-sensor feedback, or 3) the Scr is low enough, that it doesn't matter, or 4) the engine is never required to work, and/or operates as a stationary engine.
>If the computer, in response to detonation,
1) pulls timing, then fuel economy will take a hit, or
2) doesn't pull timing, then the engine may overheat and destroy itself in the long term, or just rattle the skirts off and destroy bearings, in the short term.
> Since you are on a restricted-budget, I'd recommend one of two things
1) spread the project over time and do it right, or
2) just stay home.

BTW, I love the First-generation Durangos. If they weren't so heavy, and so hard on gas in my application; I mighta bought one years ago.