Okay, so once everything was in place, all cabled-up and finally ready to ride, a disconcerting headset wobble was immediately apparent.
After a frustrating session or two failing to get the preload just right and the Gripnut tight enough, I was about ready to throw in the towel and take it into the shop.
Then a friend spotted the problem right away...
I don't know how I didn't clock it before, but if you look closely at this photo you can see that the diameter of the older No Logo cup is just a fraction wider than that of the modern GripNut top:
See the little lip on the left, where the turquoise top meets the silver cup? It was harder to see silver-on-silver, but it was definitely there.
Hardly the end of the world, but frustrating nonetheless. Especially considering all the other little battles I'd endured with this build and then only discovering it once everything else was squared away and finished!
Oh well, a trip to eBay to secure a more modern logo'd version did the trick.
One older headset removed, another slightly less old one pressed in:
And that's pretty much the whole bike done.
I'll get around to completing a full spec list eventually, and I'm hoping to have friend shoot a few photos for me on Friday, so will update this thread accordingly if successful.
I've taken a fair few myself on various rides (it's hard not to with this one!) since completing the bike, so may get restless and post some of those in the meantime.