I was amazed when Zack posted on our local page that he was starting this project. His rig was/is one of the nicest I have seen in a long time.
Personally I don't agree that you can not reliably run a mechanically injected diesel here. I love my old 6.2s It can be hard/slow to source parts for Toyota diesels here however.
A GM small block is a no brainer swap. TBI is still simple but is a step up from carbed. A 6.2 or 6.5 GM diesel is a pretty simple swap as well (We have a couple of those working their way toward happening here).
You will not need to change your gearing no matter what engine you wind up using. Depending on the tires you wind up with an how you use the rig, you may be able to and may even gain some benefits with different gearing, but those two considerations matter more than your engine selection.
I have not made the time to catch up on our local page much lately Zack, but rest assured I will be watching closely.
You can't go wrong with POR. It might be worth checking with Advanced Powdercoating out here in the Valley. They do great work and have fair/great prices. and an oven plenty big enough for that frame. they can sand blast it and powder coat it for you all at once.
These are cross posts of a couple of the pics Zack put up on our club page of what his rig looks like now.