Dismantled the Poo Brown Bike. Got 27.2mm seatpost to slide nicely after removing a lump and a few burrs. Bare frame is 4lb 10oz and it's a biggie (23 1/2") so the tubing sticker is correct and it has d/b frame tubes (rule of thumb is 4 1/2 lb for a medium frame if it's full 531DB). Found frame number, which matches fork number and dates it to 1986, much later than I expected considering it has a fork blade lamp bracket. It is a genuine Holdsworth, anyway.
Fork crown race was spectacularly loose, just falling off, and I think someone may have fitted a JIS headset by mistake. The seat is slightly undersized but a new Tange ISO crown race doesn't slip on and will require a press fit, so it's all good.
BB is a 119mm JIS taper and is actually an SKF, not a FAG. It's quite serviceable but I'll have to see what sort of chainline I get with the Exage cranks. From experience, Shimano road cranks of that age need something like a 110mm symmetrical BB BUT the SKF is asymmetric and longer on the non-drive side, so it may not be all that far off. I was going to put a 1mm spacer under the fixed cog anyway, to ensure the chainline is still correct if someone puts a freewheel on later (Shimano freewheels are about 1mm further out than a fixed cog).
Annoyingly, the bars and stem turned out to be 25.4 and the spare bars I have kicking around are 25.8, 26.0 or 31.8. The 31.8 bars are the nicest but would mean a quill converter, an A-stem and a load of unnecessary weight.
The Weinmann Vainqueur centre pulls cleaned up nicely. I will use the Tektro levers that slope gave me.