Weeeelll... I have implemented a much simpler solution that seems to be okay.
The bottom bolt that came with the plate is 1" long. I went to Lowe's and got another carriage bolt the same size but 1.5" long.
I sandwiched the wing between the plate and STA, moved the 1" bolt up to the top and put the 1.5" bolt in the bottom.
The stabilizer rods in the HOG wing seem to be just about exactly the same width apart as the width of the STA mounting plates. Or, perhaps I should say, the wing stabilizer rods are just slightly narrower. With the STA on top, the rods are right under the edges of the mounting plates.
No big deal.
I put it all together and tightened the nuts down. I don't know what the wing stabilizer rods are made out of, but they crushed down pretty well. The STA mounting plates just crushed the very ends of the wing's stabilizer bars, so no big deal at all, as far as I'm concerned. There is still plenty of rod left in there to stabilize a tank if I ever move the wing back to a conventional back plate. And I didn't have to cut my wing or remove the rods.
With the 1" bolt in the top, 1.5" in the bottom, and the wing sandwiched in there, I mounted the rig onto one of my HP100 tanks. I did this after removing the rubber hose that came installed over the STA rails. Like that, it looks like the 1" bolt at the top comes very close to touching the tank, but I think it might just barely be clearing it. It's hard to tell. The top bolt is definitely not hitting the tank and holding it away from the rails, anyway. The 1.5" bolt in the bottom comes nowhere near touching the tank and, actually, I really don't see why the bottom bolt needs to be any longer than the top bolt in any configuration. The back plate and STA mounting plate appear to be the same thickness at the top and bottom locations, so the bolts seem like they should be the same length top and bottom. As the FCP was shipped, it seems like it could have just as well had 2 bolts that were short, like the top bolt that came with it was.
Regardless, it's all together now and seems fine. If the crushed parts of the stabilizer bars are holding the STA out away from the BP by some extra amount, it definitely seems negligible. If I use it and determine that the top bolt is scratching the tank, I could just put the rubber hose back on the rails and that will surely fix it. Or, I could put a thin washer somewhere between the BP and the STA to space it out 1/16" or so.
Or, I might get a 1" wide nylon webbing cinch strap and sandwich it between the wing and STA, with the top bolt going through it, to make a tank hanger strap for hanging the whole rig on a tank, at the right height, while I do up the tank straps. That should also push the STA out just enough to ensure the top bolt doesn't scratch the tank.
Anyway, I'm taking it diving! (next weekend)
@Eric Sedletzky, the 1.5" bolt I got from Lowe's is Zinc plated, I think. I would be okay with that. But, it also has raised lettering on the bolt head. The bolts that came with the plate are totally smooth (and stainless, of course). I'm just anal enough to be slightly bothered that the raised lettering might eventually rub a blemish into my wetsuit. Where can I get another 1" bolt exactly like the one that came with my plate? I'm pretty sure 1" is long enough for the bottom bolt, even with the wing sandwiched in there.
