I went by the shop today, to check up on The Brick, and got some surprising news:
There's no electrical damage at all.
As far as they can tell, what I thought was an alternator grenade was actually just a bad engine backfire (its got headers and no exhaust currently) that caught some engine oil sludge on fire momentarily, and jarred the engine enough to temporarily break connection on the already-loose battery terminal for a few seconds.
The subsequent dead battery was another oddity that we're still trying to figure out, as follows:
There is a thin-gauge wire jumper running from the connector plug on the alternator that terminates in an alligator clip. When it is clipped onto the battery terminal, the alternator charges the battery, when it is not clipped onto the battery terminal, the alternator does nothing. (I'm kicking myself for not taking a picture of this setup).
Anyway, I dont know why its there, the only thing I can think of is these two scenarios:
1. whatever circuit this completes causes some sort of slow battery drain through the alternator, and a previous owner removed the jumper for storage, and it should be replaced with a more secure removable connection like a spade lug.
2. This was a really shittilly-done aspect of the engine swap, to make up for a missing piece of wire harness, and should be replaced with a proper permanent connection.
Anyway, with the jumper hooked up the battery charges just fine, the truck starts up and runs normally, and the junior mechanic at the shop used the truck to smash down some snow piles while testing it out. Tomorrow they start tearing the brakes apart. So far I'm somewhere around zero dollars.
As requested: a few more pictures:
Like Matsuo said, its bigger than it looks. Use other cars for scale. And keep in mind that those are 33x12.50 tires on it.