Just been out and twisted the pump towards the head and, like magic, she's cured!

Now, I feel both elated and slightly dumb at this point since timing is one of the first checks I should have made. However, with the misfire being fairly distinctly on #2 I was thrown off the scent at the first instance and based my troubleshooting around the fuel/air/compression of that cylinder alone. My only guess is that #2 has the lowest compression of the 4 (although within spec) and this was the first place the issue showed up.
I would appreciate the input of Les (White's previous owner) on the matter, most specifically when he had the cambelt replaced and if he noticed any change at this point. The tension appears fine and it's a Gates belt but my guess at the moment is the belt was replaced with the pump a tooth out (very easy to do in my experience even using pegs) and the problem started there but perhaps went unnoticed for a while. Think there's about 6k miles on the cambelt.
Anyway, I'm off now to let my excitement crossed-joy crossed-embarrassment crossed disbelief subside a while & then reassemble and properly time-up the engine when time allows. AND I can put my compression tester budget to use on some dial gauges.
(P.S. I think in my excitement I said away from the head was advancing the timing in the other post. Anyway, it's obviously the other way round given how readily she now starts and the slight increase in cold-clatter I hear).
TL:DR-: After all this time, the injection timing was just a tooth retarded...