Scratch that, my idea didn't work. I had planned to cut the stock rear mounts apart and weld a spring seat to them, but it won't flex with the shock so the spring will bow and rub the threaded sleeve. My concern was that the rear shock mount had no solid (steel) place for an upper spring seat (for a 2.5 ID spring) to rest against and I didn't want to let it rest on the thick 1" chunk of rubber that's there as part of the shock mount because it'll probably cause the shock to clunk on rebound or do something unexpected.
I bought a set of lowering springs for now (as much as I hated to cave and do that). I'll revisit coilovers later.... probably not going to make koni or bilstein based ones though, I just don't have the time for it. Getting into the busy time of year now with everyone getting their tax return money to spend on their cars, going to be working late hours just with shop work.