Lookin for a new Daily Driver.

[69C20CUSTOM]

I know its been covered before but I need some tips from you guys who have these older trucks. I had a 69 c20 but I dont know alot about this trucks.

So i was thinkin of finding a c10 longbed. I was thinkin about putting a stock 350/700R4 with a shiftkit and maybe a 3.07 rear gear. I do about 300-400 miles a week all highway so im tryin to make it highway speeds with low rpms. I want to lower the truck maybe less drag on the truck and I want to run newer chevy 20s on it. So wanted to know if that drive train combo would get some ok mpg.
Any tips would be great cause im getting tired of driveing my car and never have a truck when I need one.

Thanks for reading.