I measured it a couple of different ways and it's pretty close to 20 thousands, maybe a few thousands either way but very close to the same thickness of the spacer ring.
I took a few more pics this morning to help illustrate.
This is the spacer ring inside the housing, notice it's notch to fit around the axle.
Not in focus but this is the bearing\seal with the bearing fully seated in axle end with no spacer ring in place.
Same but with the spacer ring between back side of bearing and axle end.
I pulled the axle back out just a tad to show the race is full in the axle end but the edge of the seal is just at the edge of the axle end with the spacer ring behind the bearing. You can just see the edge of the race in this pic.
This shows the thickness of the caliper bracket that butts directly against the axle end. ID is exactly the same as the axle end.
I had one more idea this morning for a fix...tack welding one end of the spacer ring onto the retainer plate to hold it in place while I set the retaining ring in and get it started on the T bolts. Here is the spacer ring sitting on the retainer plate. The ring needs to be compressed just a tad to fit into the caliper bracket hole so I can't tack both sides...plus two completely different metal types and limited welding skills may make this a bit difficult as well.
This would fully seat the bearing race into the axle end but would make things very tight between the lug stud heads and e-brake hardware while moving my axle flanges in 20 thousands (which might make me have to run a big bigger wheel spacer to keep tire off of frame).
I really want to put that spacer ring behind the bearing. I don't see a bearing race issue but there possibly might be a bearing seal issue.
Thoughts???