rear end, engine, transmission combos? best engine rpm for mpg?

[SATX]

Hey everyone,

I'm in the process of building a '67 SWB with a 350 from a '79 ambulance and a 700R4 transmission. I have two rear ends sitting around. There is a 4.11 limited slip and a 3.73 open differential. The rear rims that came with the truck are 15x10 Convo Pros.

According to http://www.csgnetwork.com/multirpmcalc.html, a 295/50/15 with a 4.11 rear end and overdrive puts the engine rpms at 55 mph at 1991 rpm and 70 mph at 2534 rpm.

The 3.73 rear end puts 55 mph at 1807 rpm and 70 mph at 2300 rpm.

Should I buy 16" rims in order to have more options in tire sizes for the 4.11 rear end? Which rear end is the better option for this engine and transmission? What is the sweet spot for rpm's and engine efficiency? All advice is welcome. Thanks for your input.

[wibilly]

if your looking for mpg's them wide tires arn't the answer, but they sure look cool

[Boog]

The 3.73 with those short tires would be near the best combo for all around use. If you do mostly highway running then maybe a 3.42 would be better. There are so many variables you cannot pin point an absolute mileage figure. How your engine is setup, how you drive, etc. You know how it goes. It's been my findings that my 97 trucks with 350, OD trans and 3.42 gears get what I think is about as good all around as I can expect. My K1500 Burb with about a 31" tire has gotten 20 more than once all highway driving. My 97 2wd GMC pkup with 28" tall tires has gotten 19 all hway.
My stock engines pull good and run easy at 1800 to 2300 rpm.
If you play with that rpm calculator you will see how just a change in tire diameter will make a noticable difference.