The only v-brake I could find that didn't require butchery to the original bosses were the Velo Orange ones - there's a bit more on the bike's own thread here: viewtopic.php?f=6&t=365624&hilit=650b&start=10
I mentioned in my post that I had bought my then girlfriend a tourer from Overburys. Technically, it was branded "Andy Powell". She hasn't used it a lot over the intervening 35 years, but her husband recently had it restored to be as close as the original as he could get it. Nothing particularly special at this point - just your bog-standard custom handmade 531 700c tourer, but ... they were and are nice bikes, eh?
Yes, I'd go with late '88...since it still has a rollercam, but has changed over from the Reynolds double bend chainstays to the Columbus single bend oval ones.