Jaake, I think that you are correct in your thinking that this is a Stan Pike frame..Stan was well known for building excellent frames..and also for specialising to a certain extent in time-trial models, which is what your obviously is..with its short rear triangle, shot-in stays, and upright angles. Judging from the frame No, the frame could well be the 91st, assuming that Stan numbered consecutively.
On the CR site there is a site dedicated to Stan's frames..and one of them belongs to Wayne Bingham, very much a stalwart on the CR List. Perhaps Wayne could check out the number and style of the Frame No on his bike.
Hope this helps a little
Norris Lockley...Settle Uk