The Norton made the round trip without needing me to take out a single spanner, so I'm thrilled about that. I've now done about 1000km (is that 600 miles?) since I've rebuilt the top end, so I'd say that's a decent test to see what needs attention. There is excessive noise coming from somewhere within the valvetrain, but not always: when the engine is hot, and when it is accelerating, under load, it sounds as though the valves (I'd say on cylinder 1) were far too loose. Then if I back off the throttle it disappears and the engine runs very smoothly. The guys confirmed that there is no smoke whatsoever coming from the exhausts, and I don't think the noise I'm hearing is piston slap.
The noise doesn't seem to impair performance in any way whatsoever, and I think that if I'd lost a valve adjuster, or bent a valve, or a pushrod, I would have known about it.
So, I'll check a few things, test ride again and report when I have an answer.
Still, nice to know I've done a good enough job to take me there and back again.