My '96WG has a 1HD VIN. Had a mph speedo when I bought it used from a dealer.
The 5HD is for models built for exporting from the USA while the 1HD are USA Domestic (so my FXR is a 1HD as it was imported into NZ years ago)
Somepoint shortly after introduction of Twin Cams is the closest I know.
Good on you John, thanks.
If the speedo was in MPH then its was an imported model.