i think fender had a belt sander set-up that was the same length of the carve and rolled the whole thing in on that without rough carving first
they were quite round up until a new member of staff started in 57 who did it a bit differently and the V-profile was born, not on all guitars and not for very long - just the ones carved by one member of staff whilst he was learning as far as anyone can tell. if it wasnt for clappo they probably never would have made a comeback
I have actually played what is believed to be one of the first 57 V necks and it is so pronounced you would have thought they would have scrapped it - but it did feel good and changed my view on V profiles - at least for chord work.
anyway, the point is that whatever they were doing allowed for a lot of variation and the style or carves, particularly at the transitions, does point towards a large belt sander. they may well have roughed in with a duplicarver but i dont think you would get as much variation if you were just sanding off the duplicarver marks. i do believe that is what gibson did though.
now onto the turned neck idea, I am sure its been done and i think it may have been one of the british builders like shergold or similar. I believe it was 2 necks in a single blank, turn the shaft then split down the middle, route a truss rod slot and attach a fretboard. I wish i could remember for sure, but it always seemed like a very silly way of doing things to me