Apparently these were dealer installed. Some factory, which MAY be limited to govt. trucks. I'm guessing they were dealer installed varying on State requirements.
Anyway, I wanted to sample fit one onto my core support. This is my "bad" tank. Pretty sure I have a recipe for that stain. Anyway, below are the instructions. The way I read it the top mounting hole is 8.5/8" higher than the horn hole. Well, I dropped it near 1/2", because I wanted it below the ridge on the core support. Contributed to that, the instructions call for a 3/8" tilt. I don't know, I prefer things upright, though 3/8" isn't that noticeable. The tilt provides added clearance and it's more or less consistent with the slope in the top of the core support. That and you can bend the bracket.
There's not much clearance between the port in the tank and the low horn. Maybe 1.25"........It would work fine as is, though the hose may rest on the horn. I don't want any pressure on that port, and there's a lot of real estate on the LH side, especially without a voltage regulator. So I'm making a 4x4ish" plate as an option, probably aluminum. That will add up to 2" more clearance to the left, and really, more clearance in every direction. Very little of the plate will be visible, if at all.
Not exactly rocket science, but glad to have finally figured it out so I can pull the radiator. Zepplin was real helpful.................BTW, free 4-core radiator un-shipped. It's not truck correct, but it works less the port for a heater hose on a BBC........Doesn't fit the shroud.
