It's just that I thought the frame looks early 90s, I thought non-threaded ones came along a little later than that.
If it is an early setup, it could be a 1" non-threaded. I had some Prolites, the headset and a Hoffman stem, all in 1", I think it was sort of a transition period.
When I bought a 1.1/8" frame later on, it was a nightmare finding some adaptor cups to save me buying a completely new front end.