More work today to find out what's happening.
I dragged out another frame,late K0 or K1, for a comparison. The K0 and a K2+ swingarm both fit the same in the frame. The distance between the rear fender mounts and the muffler hangers are the same on the K0 frame and the other one. So, to keep things all the same for comparison I used a spare hub, the same pivot bolt, collar and end caps, axle, spacers, chain tensioners, sprocket carrier and brake hub for each "test". I installed the suspect K0 swingarm and then installed the hub assembly. From the pictures you'll see I found the centre point on the top fender mount/cross piece, between the fender mounts and the hub. I also put a level across the frame at the battery box area. I fashioned a mm plumb bob as well.
With the suspect swingarm, the centre of the hub is about a 1/4" to the right of the centre of the frame and fender mounts, like before.
With the K2+ swingarm it's the same. What a surprise!
So, the suspect swingarm may be ok. I had the K2+ swingarm in a K1 and it rode nicely so it should be straight.
The frame does not show as marks from a major hit in the rear area.
I'm now left with: the frame was built this way, I'm too anal again, or the frame is tweaked but doesn't have any visible reason where and why, just put it together and forget it (the off centre rear fender will be a conversation starter, of find another K0 somewhere for comparison, start again with a new frame.
Or, take it to a pro and see what he says.
I have not as yet checked the wheel alignment from the front one to the rear. I have to find a long straight piece of metal to this and Home Depot didn't have any yesterday.
Thanks for reading this long post.
Any more ideas out there? Am I missing something so obvious/simple I can't see it?
Cliff.