Got the group components back from the machine shop. They cleaned up really well, and as others have noted, glass bead blasting gives a matte finish. I really like it, and it makes me wish I could have had the pistons blasted as well.
The pitting on one of the spring surrounds is quite bad...but since these are unobtanium, I'll just have to make it work. The area you can see where the bolt hole is just gone in one section, is not of consequence as those are only for attaching the plastic spring covers, which I never intended on installing anyway (I prefer the exposed spring look). One of the piston rods is also more pitted than the other, so I'll likely rebuild the more pitted components together and just consider that the 'backup group' and minimize use.
The bronze group bores cleaned up amazingly well. They taped off the bore itself since those were already cleaned up nicely and they didn't want to inadvertently strip the finish off inside it.
Anyone have any thoughts on a clear coat I could put on the spring surrounds to at least prevent further degradation? Now it will be running on Seattle water (which is very soft), and I'll have a filter system between the water supply and the boiler. Still, it seems prudent to try to contain/seal the corroded areas against further damage.