Of course it won't, but why?
I was honestly under no illusion that - having done all that I have done - the bike would just start, nevermind first kick, although it is possible and much more common than you might think.
Let's examine the situation: I had recently adjusted the valves, we have good compression, sparks and fuel at least into the float bowls. Timing has not been altered since the bike last ran, and ran it did, so...
Kicking it over, the engine turns freely (albeit a little stiff, but that's to be expected with new pistons, rings, etc.). However, when checking the sparking plugs, they are bone dry without even the faintest trace of petrol on them. So, gas ain't getting through.
Off with the jets assemblies first; result: jets were not perfectly clean (though I have seen much worse) so I cleaned them. The same goes for the idling circuit, so of course I removed the air screws then set them back at 1.5 turns from fully seated.
Again, it won't start, though there is an audible combustion happening in the number 1 cylinder, just once.
So, why won't it start then??!
Well, the only thing I had not double checked was the valves, which I thought were adjusted properly.
And therein lies the mistake: this is a reminder to never assume anything, never take anything for granted with these machines. The moment you are sure of something without having just double and triple checked it, go check it. I guarantee you'll find a problem. So, I re-adjusted the valves following the Workshop Manual to the letter, then put everything back together as it should be.
Oh by the way, it starts now. First kick.