Nice! There's a Corvette build that should be enlightening if I were to do the same for my 1980 Buick. I often think a small diesel might be in order if the engine ever needs to be replaced.
Yeah, most major and even most minor modifications cannot pay for themselves...all you can do is take opportunities when a part fails and needs to be replaced anyway.
Doesn't the VW truck share many parts with the Rabbit of the era? Maybe that doesn't help much in parts availbility, but it is probably easier to drop a TDI into than a Toyota. An original diesel might even be found.