Thanks for the update. I have a Strada with that exact running gear. Pretty sure my bike is a 1991/1992 model. I really love the profile of the wheels but I haven't ever seen any others like them, so I'm really trying to look after them.
Just to fill in some gaps. The 6-speed Shimano is the older uniglide system in the hub. It's long discontinued but NOS comes up on eBay frequently for sensible money and there seem to be a number of new cassettes that come up from time to time. I've only had occasional problems with the ratchet in the freewheel, but a strip down, soak and re-oil fixes it so I've not needed to replace it. It's a nice nearly silent ratchet as well.
More info on uniglide here: http://www.sheldonbrown.com/k7.html
I decided not to replace anything because, with the indexed shifters, it looks like the whole lot has to be changed.
Nice running gear though. It's smooth and fast. Shimano 105 SLR brake levers are a direct replacement for when the Exage ones get damaged.