diesel drive train ?

So I am noticing how high my rpms are with my 5spd and r-200 setup at speeds like 60 - 80 mph. These are typical speeds around here in the fast lane. I am taching 3K @ 60 and 4K @ 80mph. Not so good on mileage but it is better than most. I am trying to figure out what I should run with a diesel. I've decided I am going to use a late Z31 turbo on the LD28. I still don't know how much boost. I really would love to be taching around 2.5K rpm @75.This would be optimal as far as I can tell. What should I think about running at. I need to get good mileage but I am going to make this a preformance beast. So a compromise set closer to preformance is what I want.

I was thinking of running something like a 3.36 or a 3.545 rear end. I will have enough torque to not worry about low gearing right? Tranny? I have no clue. I'm going to be playing around with the tranny calc. and see what I can find, but I have no idea what the trannys are running inside.

thanks:

Ray