lets go for mpg on a c20

[superkingd]

Okay to start we don't buy these trucks for mileage. However I want to drive mine more. I commute 50 miles a day and don't want to buy a 4 cyl for 1000 and end up buying someone else's used turd. So here we go.

1970 c20
355 th400
it had a great running 292 inline 6 and granny 4
I have a 700 r4 I could rebuild
Also has the Eaton rear axle but I have a 3:55 geared ford 9 inch.

Here are the thoughts
I could put a tbi set up (stock gm) on the 6 with a Clifford intake.
And mate that to a 700.
Or tbi on a 355 and 700r
The inline 6 would be pretty cool.
anybody tried any of this with luck
My goal which may be tough is 20 mpg.