Exactly why I'm not using a blowtorch.

A heat gun is getting the parts to maybe 200°, sufrace temp is likely a little higher. 200° isn't bad considering some shocks can overheat beyond that with extremely hard use. And, this aluminum casing wicks away the heat REALLY fast, so only the steel bracket is staying hot.

I still can't break it loose by hand, and the lockrings are getting rather chewed up from me using them for leverage.

So, I brought it into work today, and our machine shop guys are going to help me. We're going to machine a ~50mm hole into a solid block of aluminum, with a slot cut into one side. This will allow the aluminum block to clamp very tightly evenly around the outside of the shock body without creating any side pressure. We're going to make the clamp as long as possible to increase surface area to avoid marring any threads. We'll clamp the block into a vice and use a breaker bar on the lower strut mount. THAT should work, the biggest problem right now is that I simply can't get enough leverage to break beyond the surface tension of the rust. I'll take pics when it's all finished.

Worst case scenario, we mar the threads and I still can't use it. Either way, if I can't get them apart they will remain completely useless as-is.

There is some good news... Disassembly of these coilovers (aside from this problem) is REALLY easy. Removal, disassembly, cleaning, reassembly, and reinstallation only takes about 30 minutes per corner. So long as you don't adjust anything, alignment should be unaffected. This is nice considering all the gravel dust and mag chloride thats caked on over the winter.