Hey Dan,
Not sure if I would really do anything different, hindsight is 20-20 but I try to do the best I can at any given time, so the job I did was the job I did.

But:
First thing I would do different is paint it grey.

We mis our grey body.
On that same note, I maybe should have found a better body, this one has some bends and bumps and had more rust around the window frame than I thought (old bad repairs, hard to spot in the harsh mid-day sun on faded paint) Also replacing the rear sill was more work than it was worth, etc.
I don't think I would powder coat the frame.
I was on the fence about it at the time but went with it for simplicity, a good epoxy primer would have been just as good if not better. The acid dip was great though.
I should have rebuilt the engine at the same time I guess.
The HZ has always been fine on long hills, it makes heat, but if it starts to get hot, a tiny bit less skinny pedal and it cools right down. You can pretty much always go up most any hill at the speed limit without getting too hot, you might not be able to pass on all hills without too much heat though.
Be careful when bedlining the bottom of the truck, you'll notice I didn't bother doing so, I find that in most cases it seals in more than it keeps out. If you go with it just make sure everything can drain still and you don't seal anything up. Bedlining the bottom of the truck is like sealing the lowest few rows of shingles on a roof. Where is the water that gets in above supposed to go?
Other than that, get ATF in any pinch welds you can get to. I still see that stuff seeping out of "sealed" seems a year later.
KR