I think there were two versions as there were changes made later in the production run. Definitely 1 inch and 1 1/8 - which seem elusive (in the sense that they seem even more rare than the already rare fork in itself).
Not sure if the removeable disc mount was a later addition or not, but it was quite agricultural and spoilt the very pretty lines. Disc "readiness" would probably point to mid/late 90's. I'd reckon 95-97. They weren't in the 94 MBUK group test, but that doesn't mean they weren't around.
I've heard they're pretty plush, but reckon they could be quite flexy (not unusual for a mid 90's suspension fork). Seemed a massive leap for USE at the time, and don't know if they used proprietary internals or it was all their own design.
I'd love a set for my P7.