[Zoomad75]

4bt's are strong little engines. Actually they aren't that little. Think of a 5.9 with 2 cylinders missing. We used to use them in Step vans, but I can't remember mileage numbers though. 35 mpg seems very optimistic to me. I'm thinking low 20s in a heavy truck.

Diesel Power magazine has an article on a 4bt conversion in an early bronco with some pretty good details.

One thing I can think of is if you get one from a step van application (GM or Workhorse) they should have the adapter to bolt up to the Chevy bellhousing pattern.

Don't overlook the 6.5's. They can be built with some better than stock numbers and still get mpg's in the low 20's. There are some good sources on the web for the 6.5's too.

Each has pro's and con's it's up to you.