I agree wholeheartedly, rear end swap should be the way to go, but he asked about engine swaps, that BPOBB should just lug along with the right gears. You could easily get away with 3.08s (or even higher like 2.73s) with all that torque and most likely bring your mileage into the high teens if you can keep your foot out of it. Also a properly built 2004r (like one out of a cadillac fleetwood) would give you the OD without a lot of expense, again, just sell the BPO TH400 for the cost of the 2004r.
Chris
