New head bearings have returned the bike to its former self - no more uncertainty from the front end.
The 750 was fun to thrash, and the quickshifter makes sense when going for it, but riding more sedately reveals a big issue with the fuelling. It's impossible to go at a steady speed on small throttle openings without it gently but permanently lurching. It's what I'd call "hunting" but not sure if that's the correct term. At first I thought it might be an issue with a very sensitive throttle that I was moving inadvertently, but it's the same with cruise control.
As I use my bike for a mostly motorway commute, I think it would drive me mad.
Other than that, it was nice enough. Maybe I'll wait for a couple of years to see if this is ironed out.
Next issue with the trusty 700: the dealers told me the front brake pads were close to limit. I bought new ones in local bike shop, fitted them yesterday afternoon, and ... brakes binding on one disc and a feeling of sponginess inexplicable sponginess - the worst kind - because I hadn't opened the fluid circuit at all. Initially i thought it might be a sticking piston, but another quick look and clean and they seemed to be ok, but still binding slightly. Then thought maybe there was too much fluid, so removed some from the master cylinder. Still no change.
More investigation soon revealed that the sliding caliper mount wasn't sliding at all. The left caliper slid like a dream, and could be eased apart by hand with minimal effort. The right didn't move at all. Getting the caliper of the pins was a right bastard - it was the top pin that was stuck, and I could only move the caliper around the pin (if that makes sense) by a few mm. If I could get the bottom pin out, I could twist it round further to free it up, but you can't remove the bottom pin with the top stuck... Judicious use of hammer and screwdriver freed it JUST enough to get the mount passed the loosened lower pin, and that allowed me to remove it. The top pin was completely dry, very rusty and stiff, in contrast to the left caliper which was still nicely greased and in perfect condition.
Quick clean with emery cloth, lubed up with high melting point grease, and all done. Spongy feeling gone too. Tomorrow's trip to Croydon should confirm whether or not it's all perfect!
I was initially confused as to why the problem hadn't manifested itself before, as the pins have clearly been seized for some time. I think that with worn pads in there was probably enough pay in the floating discs to stop any dragging, but the extra thickness of news pads meant that it needed the calipers to slide as designed. Anyway, it's sorted now and I've made a mental note to grease the pins every couple of months to prevent recurrence.