Hi AlasdairE,
The forks I used on mine have a 1 inch steerer - you can still come by them secondhand - I got lucky with the Deda Black Force Carbon's.
As for modern group sets - I've actually just converted mine to Shimano 105 compact. The BB is a fairly standard Shimano English Threaded...
Great to hear that you still have your R500 and that it's on the road again. I'll definitely send some pics of mine. Been waiting for a decent day and also having snapped a spoke at the weekend, the wheel was being sorted and is now back on. [And the bike cleaned!]. Will be in touch. I may have...
Re: Caad2 R500
I've kept a link to this post for years as I have the same bike. Always thought it looked great and your post gave me a kick to sort mine out and use it more. I've had to upgrade parts over the years as I was using it as my main bike up until last April. Now it's my winter bike...