In case anyone is interested, here is a view of the rig I am playing with now. Very similar to Peter's using a Nikon PS-5 stage and major RRS parts, but using a 100mm macro (on full frame). I took advantage of a few RRS parts I had in the drawer.
John

also here are photos of the PS-5 as stock and disassembled


and undergoing modification to remove flange

John