I think there has been discussion before about the differently shaped Baldwin Marvins ('prototypes') used by Hank and Bruce on the Oz tour in the mid/late '60's..
Not only were the bodies differently shaped, but also the scratchplates, and they also seemed to have a different control setup- four knobs only, rather than the three knobs and selector switch used on the preceding Burns Marvins.
I was just watching a youtube review of the reissue 1962 Burns Bison, which has the four knob setup- as did the second version of the Bison which came after the original 4 pickup model.
As far as I am aware, the Bison circuit differed from the Marvin circuit, in that the four knobs were master tone, master volume, two way rotary switch to change circuits, and a four position rotary pickup selector- giving eight different settings.
I wonder whether those Oz tour guitars had Bison wiring rather than Burns Marvin?
Thank you!