Hypothetical build questions…

i think cam selection is going to be critical here. you're working with somewhat diametrically opposed forces: a big valve, high(ish) compression motor that wants to spin and make power uptown; and an OD crash box that has kinda crappy ratios to stay in what could be a narrow power band that also is going to eat into that rpm where you make power while at cruise.

i think anything less than 3.55 you're going to have a dog at highway speed. with OD you'll only be clicking about 2200 and that's where that type of motor just starts to get cooking.

i'm with RRR here, a smaller cam without a radical profile would probably do better for what you're trying to achieve. carb as well, small and vacuum secondaries.

also, keep in mind that the OD boxes don't like a ton of power put to them without some upgrades they won't last.

edited, i didn't see that the OD box was an iron unit. disregard and carry on.