I finally got around to "finishing" him. I say that in quotes because I have the bad habit of taking projects like this to about 90-95% and stopping. In this case, though, It's because he needs some repainting, because a chunks of his paint peeled off as I was manipulating him during the mods, and I am helpless at painting.
Regardless, here's what I finished up with:


The crane's base can swivel, so you can put the crane arm further back or forward, depending on the job:

Bot mode; the hand can be replaced with the little cannon-thing:


Here's what I did myself:
-Attached the crane in both modes. For the alt mode, I installed a pair of pegs in the floor of the bed, which mate with holes in the bottom of the crane assembly. I mounted the crane on his robot-mode back with a small pair of hooks that hang onto the edge of the back panel (the windshield). It just hangs there, so it's not secure, but it's all I could come up with without spending a lot more time on it.
-The wings drop into the space between the crane and the front of the bed in alt mode, but I might try to put them up on top like G1 Hoist. For robot mode, they peg (rather cleverly, I think) into existing holes on the top edge of the backpack, in roughly the same location as G1. They are pretty long, though, I might shorten them up.
-Mounted Alt Hound’s wheels and tires (really happy with how they look!). I picked up a loose set of them, and they’re the same overall size as Prime’s, so it was pretty straightforward. The axle is smaller than Hounds, so I had to make a sleeve (from the corrugated part of a bendy straw!) to fill in the gap.
Here's the rest of what I want to do:
-“Un-pimp” the alt mode. It’s a sport truck, which to me doesn’t suit Hoist very much, so in addition to the more workaday wheels from Hound, I removed the rear wing, and plan to mod the front end to make it look more plain.
-Add a tow truck light bar and other details. I’ll have to find a 1/24th scale truck to take one from, and I will scavenge whatever else might look good, like chrome mirrors, toolboxes, etc. Maybe add some fake diamond plate.
-G1 Hoist-style graphics, the black/yellow hash marks down the side. These I’ll have to make myself, should be fun, in the same way that defusing a bomb might be: could go well, could be awful.
After all that, I'll have to fix the paint, which I am not looking forward to. I'll try to find some brush paint and slap it on, I'm hopeless with a spray can. It would need to be painted with a flex agent mixed in, really.
Your thoughts and comments/suggestions, please!