As for the 86 parts, I thought the aforementioned items might make the conversion to the 2.8 easier, while retaining a somewhat 'stock' look and using Isuzu parts to ease the sourcing of spares in the future (probably futile, but what the hey).

I'm going to order the 2.8 through an importer in Florida, complete with transmission and all accessories.

The NPR filter idea sounds like a good one. I am also considering an aftermarket setup (racor or similar). I will be converting it to burn veggie oil, so I will need another filter at some point. I thought a stock Isuzu filter would ease the conversion process byb using (hopefully) bolt-on components.

I'd like to keep the power brakes, as this is going to be a daily driver. The 2.8 does come with a vac. pump, so I'll use that. It it fails, I would consider the option of going with hydraulic GM assist, although I have no idea regarding fitment. I've seen the setup before, but haven't measured anything.

Any suggestions as far as radiator is concerned? I think the inlet/outlets of the 2.6 rad are in the wrong places -- it's really a moot point, though, as it seems too small for the diesel, which likely requires a larger radiator. Something from a V8 CJ Jeep perhaps? I am trying to think of something thick but not terribly wide...

The 6.2 sounds like a great project. I'd like to hear more if you decide to tear into it. As to the Mercedes engine, I owned one in a 300D turbo sedan for a while. Excellent engineering. I wonder how a truck would deal with its power curve, though -- high redline and all. Not sure of the torque output and at what RPM it peaks. I know people have used these as swap engines before (at least the 4cyl. diesel from MB).