Are yo utalking about the "sliders" that fit the seat to the floor, or are you talking about the seat-back rake adjuster? The series I changed from a 3.8 to a 4.2 Litre sometime in late 64 I think, and around that same time the seat style changed from a "bucket" style seat with a rounded back to a more comfortable square-backed style. I would think that any of these parts from any 4.2 series 1 or 2 would work, from 64/65 to 68/69 but not so sure if the parts from the earlier style seats would work. They may, I'm just not sure.
Basil
67 Etype OTS