Some of this is great thinking I a am sure but am unable to wrap my mind around some of the concepts as I read them.
Concerning the use of centers.
It's going to be very difficult to drive this between centers due the difficulty (as I imagine it) in ensuring a precisely equal relationships between the two shafts. One shaft could be rotated slightly more or less then the other, that won't work.
The more I think on this the more I see the necessity of a rotating fixture to precisely hold the block as the shaft is turned and then the block rotated to do the other end, this concept has been mentioned in way I don't understand as yet.