No, our 1FZs are almost certainly not making less than 141hp at the crank, unless severely disabled. Sure, one may have been dynoed at 110, but that must have been at the wheels.. and any engine swapped in will have its own drivetrain losses. If you go with a manual it'll help a lot, but the transfer case (gears, not efficient) and axles are still going to hurt things with ANY engine.
But... my point is that with the ridiculous cost of these setups my gut is telling me that even stock wheel horsepower isn't going to be worth the money.. and 168 at the crank will struggle to overcome a 45hp deficit even with a more efficient transmission and fresher engine in the mix.
And, I just realized.. add the cost of taller gears (if they are even available) to get the most of that freeway mileage. Even 315s with stock gears won't get you close to ideal freeway RPMs for a diesel with the overdrive ratios commonly available.