Beautiful. Not unlike my own that is still going strong.
I note yours has braze ons for a rack on the seat stays. Number wise I cant comment with the AR which may indicate who actually did the frame building for Harry on yours. Since I reckon they had around 50-100 frames a year built, then 1590 would probably put it as mid to late 1980s perhaps, but am prepared to be corrected. Yours seems to have lost its HH seat tube transfers and any Reynolds (or other tubing transfers on the seat tube and forks.
I believe Harry imported some frames from Italy as well as having some built by the likes of other framebuilders such as Woodrups and Bob Jacksons in Leeds. I do recall however an article once (cycling weekly??) on Harry’s set up on Cathedral Street and having a frame jig set up in the Corn Exchange buildings behind for limited use in one off builds and repairs. Does anyone recall that article?
I note yours also has the drain hole on the BB - at the time I was ordering mine, Harry was keen on ‘vented’ / ‘slotted’ BB shells to allow moisture out. I was more intent on keeping moisture out at this vulnerable spot and had elected to have a sealed bearing BB axle (Nadax - via RJ Chicken distributors). So there was me in my younger days telling a TdF mechanic how a bike should be! Still it has lasted thirty seven years maintenance free, so perhaps I had a point!
Oh and you might find the colour was described at the time as Grigio Grey. They did a gunmetal and also silver finishes too, myself having previously had one of the latter.