So I pulled the heads, and it looks like the other valves all need replacement. I kinda figured that. But here's my next question. I was looking at the guides, and they still seem in spec, but I found it off that none of them had the retainer clips. Also the grooves for the clips were 2-3mm above the valve head. Has anyone else ever run across this? it is consistent across all guides.

Definitely clean and inspect the bearing races. If there are any skid marks, corrosion or (likely) little ribs in them where the rollers have 'sat', swap them out.

As for tension, yes, tighten lightly with a spanner (spart plug sort of tight) then back off a little. The steering should drift from side to side easily, but with no looseness. I didn't have to do ant twiddling of the top nut once set, as the threads are quite tight and fine.

I did this a few weeks ago on my 1979 R65. My advice is that having got this far you remove the top nut, separate the yokes, and clean out all the (likely disgusting and solid) old grease that you will find. You can then repack the bearings with a suitable grease (not wheel bearing grease, which won't warm up properly) and tighten down.

I followed the Clymer advice that you have found and after torquing down the top nut it was too tight. It took a few goes backing it off, backing the knurled not off a little, retorquing etc. until it felt right.

Note that the screwing down really tight of the knurled nut, then backing it off again, is especially important if you have regreased the bearings as you need to preload them before backing off to running torque. And I suspect that is what Clymer is really trying to say.

At this point I have the front wheel off, forks pulled to change oil, and the front end ready for adjustment.  I have the top allen bolt loose and was able to crack loose the finely notched adjustment 'collar'.  Based on the effort I can only image it was too tight and the steering felt stiff before I started.  As I tighten and adjust the collar how to I know when to stop?  Right now the bearings are smooth, turning is light, but it's hard to know how to get it set just right with everything off the front end and the dash hanging of the front. 

EDIT:  Think I just found my answer in the Clymer manual.  Tighten the adjustment nut by hand and then loosen until "free play is all but eliminated".  After reading this the bearings were WAY too tight from the PO.

My 1979 R65 needs new tyres for its 18" snowflake rims, if only because the current tires that it came with are over 20 years old.

The Conti Classic Attack by Continental is well reviewed, so my thought is to fit 90/90 R18 on the front, and 110/90 R18 on the rear. My question is whether anybody has done this before, because the 4.00x18 that I took off the rear was tight, and 110 is theoretically is a little wider still.

Does anybody have a 110/90 R18 on the rear of their twin shock R65?

Also, given that I'm not comfortable using the 47 year old snowflake rims tubeless, I'd appreciate experiences of those who have used them with tubes.