Ok, I couldn't stand the suspense so I went home at lunch and looked at the parts. Here is what I have:
061917 upper yoke on both my 750 and my 850
061916 lower yoke on both bikes
The (presumably) 850 yokes have the following numbers:
ANG 064084 upper yoke
ANG 064083 lower yoke
Looking at the bikes, the fork tubes and headstock appear parallel with the 750 yokes. I held up a carpenter's square and they still looked parallel by eye.
Next, I slid a new, straight fork stanchion into the 850 triples. It was immediately obvious that the stanchion and stem were NOT parallel, with the forks being pulled in to a steeper angle than the steering stem.
I then took some measurements of the distance from the stem centerline to the centerline of the stanchions, using the carpenter's square and a cheesy Harbor Freight plastic calipers.
Those measurements are:
061917 750 upper: 65 mm
064084 850 upper: 72 mm
064083 850 lower: 69 mm
I did not measure the 750 lower yoke offset but it appears to be the same as the 750 upper.
So what is the 061917 part and how does it differ from the 061915 part? I believe one difference is the threading on the end of the stem. When I was restoring my 750 I bought a nice new nut from OldBritts. It did not fit - wrong thread pitch. So I sent it back, asking if he could exchange it for the correct one. Fred replied that was the only one there was, he tried it on a couple of stems and it fit perfectly, and hence there would be no exchange or refund. He sent it back and I binned it and reused the old nut. I'll bet it would fit the stem on my 064084 yoke. I'll probably have to buy another one when I put those yokes on the bike.
Another little observation is that on all the parts, the numbers are cast in, not stamped.
I did not measure the distance from the stem to the steering lock on any of these parts, as that would not seem to have any relevance to steering geometry, only to whether or not the steering lock would fit properly. I don't have a steering lock fitted to either of my bikes.
So there you have it, everything I know at this point in time! :mrgreen:
Debby