1" threaded headset sizing, ISO or JIS?

I have this http://www.londonfgss.com/thread4622.html viking track frame bought from hammo, I need to get a new headset. How do I find out what size crown race it has without removing the crown race and measuring with calipers? - I fear that the crown race might be damaged with removal, hence a reluctance to do this yet - I need to ride the bike every day.
The headset is has at the moment is an Edco competion.

nice strong little frame. just whack it out, hard to damage.

Basically, JIS headsets came on Japanese and Taiwanese frames. There are a few exceptions, but a 1960s British bike is going to have a BSC (ISO) headset. If you want to be sure, just tap the crown race off and measure. Go gently and you won't damage anything.

JIS 27.0 :: ISO 26.4 I think.

heres a link for a new Edco Headset, pricey tho..eeeek
http://www.bicycleclassics.com/headsets.html

Thanks for your replies so far. I took the headset apart and measured - It's ISO. However, in doing this I realised that the bottom of the head tube is at a fair old angle and the cup isn't sitting flush,probably the result of being ridden for a while with a loose headset - so I think it needs facing. Which bike shops in London do this and how much do you think it would cost?

most will do this, where are you based?

E10 - leyton, so London Fields is prob closest - how long does such a process take?