Right, bit of an update. Still have not found out exactly what's going on with this one but am beginning to doubt it's a hand built frame as I've found a serial number on the seat tube.
Looking at other Clockworks from around 89/90 this frame does have some different features that would suggest it may be some sort of prototype though (front mech cable routed under bb instead of a noodle on the bb + other differences). The down tube is wider then the top tube/seat tube and I can't remember my others being like that? The forks also seem to be a bit chunkier then others I've had and the stem not like other Orange ones from the time. I'm leaning towards it being a limited run from the factory to test certain ideas, maybe then given to employees to test? The proto decals were obviously fitted at the same time as the usual ones as they have dated just the same. Very confusing.
I've stripped it down and degreased and the paint's come up better then expected. Seat post's stuck for now but I've not tried very hard to free it. The stem was also stuck but came free with a little effort.
Anyway, finding the serial number has made me lose a bit of interest as it's got a bit too much patina for me to use as is and I'm not really in to repaints atm so think I'll move it on. Hopefully the new owner will be able to get to the bottom of it's history.