Hi all!
I'm in the middle of restoring/upgrading/modernizing my 1973 IH Travelette.
For those of you unfamiliar with light duty Internationals, it's a 3/4ton rated, 6,700lb crewcab, I've added little doodads like 1ton springs 4wd, dually rear(as I recall it's a dana 70 with 3.53 gear) dana 60 front.

My question is, what engine would you put in such a beast? I'm pretty comfortable with Gm 6.2ls but I'd like to keep it all International, like a 6.9 7.3 or DT-466. But at the moment mileage is more of a concern for me. I am told that a correctly tuned Cummins 5.9 is capable of near 30mpg.

I'm looking for the best compromise between power, reliability, but most importantly mileage.

any input is very appreciated!