I'm still not convinced because Gary at Brezelwerks claims in his add on the Samba, they're used up to '55? (with all respect for Gary)
Come on, if you ask me he's also sort of guessing.
My personal opinion is that they followed the improvements with plastic technology of the time. Why would they change the wiring harness to plastic? Because it was cheaper and easier to produce imo.
So I think the gradual change was a lot earlier ie. zwitter era.
But as I said, I can't back it up.:x
Proost! Peter.
1954 Oval L275 (in progressive refinement)