Mike,just my 2 cts.worth.The 350 and 700R4 is a very good way to go for mileage.Thats what I am running with a 3:90 rearend and Im getting 20 MPG.If you go with any engine,454,0r 350 and a 400 turbo,your gonna have to go to about a 3:08 rearend to get good mileage.The 700R4 is an overdrive tranny going about .78 to 1 to the rearend whereas the 400 Turbo is 1 to 1 ratio. Hope this helps.
