Just a quick note. The threaded insert type head is a long Track head. It was done to allow larger inlet ports to be used if required, if you look you will see on the threaded type there is no `recess` for the nut to fit on a stud, as in the speedway type. Larger ports were ok on the LT and some GTs but smaller ports were found to produce a smoother `bottom end`.....more suited to speedway, so the speedway type is most common on, suprisingly, speedway! You could order a Weslake 500 with either speedway or Longtrack type head, its not necessary a way to tell th MK of engine.
