Did you get the crown-race off the forks? many (not all) have the dimension (26.4) engraved underneath. I wouldn't think a Dawes Galaxy would be JIS, but you never know... anyway, it's easier to be sure of 0.6mm discrepancy (crown-race) than 0.2mm (headtube sleeves). I don't want to second-guess your calipers, but obviously reaming is irreversible, so, you know.. be certain of the measure before commiting yourself to the cut.
Also, the headset I removed seemed to have the ball races built into the top & bottom cups! As I've not much experience with 1" threaded headsets, I don't know if this is normal or not.
Your headset does sound unusual, I've not had much experience with anything but
1" threaded headsets, but probably a pretty small sample of the range of variations possible- I don't remember ever encountering captive bearings.. but again, you never know..
Many thnaks for your reply
It's defiantly a 27mm fork race & I couldn't see any measurement stamped anywhere on the fork! I thought the bearing races most unusual, but have mostly delt with 1 1/8" threadless headsets before (coming from mid to late 90's mountainbikes)
I will try to get a photo of the headset up sometime this week & will carry on with the stripping of the paint.
PS... I've heard vernier calipers called "very near" calipers before, so I understand what you mean.
apparently I've read on the web that some people think it's OK to press a 30.2mm cup into a 30.0mm headtube!
The internet seems to have turned people into experts overnight!
MANY thanks for your valuable advice