I'm pleased with this conversion. Last long trip it easily got over 20mpg.
I've had it to 135mph and still pulling. The engine is a GM crate motor with a cam upgrade, aluminum intake and holly 600cfm carb. It idles well with a slight hint of "cam". Torque RPM range is pretty wide and smooth.
The original six differential failed during a "standing on the throttle second gear shift". I replaced it with one from a 4.5 W108.
The car handles very well however, recently I've found the subframe bushings worn.
Its currently undergoing an engine bay cleanup (rerouting some wires and hoses), new AC system. There's a ton of room to work.
Subframe bushings soon.

I sill wish it was a diesel though... Love to swap it for a nice TD. I've got more things than A$$ to haul these days.