Thanks very much for your reply,

The lenses I intend to mount are 105 and 150 rodagons for now and a 180 or 210 later for 5 x 7. Can I not get machined a bevelled edge disc that fits in the unipla, with a threaded hole in the center to suit the lens ie 50mm x 0.75 for the 150 rodagon? I realise that some have a top hat design and this increases the distance between neg and film..cannot remember if this is for very small ir very large enlargements...but can I get away with a flat disc?

A local precision engineer quoted 50 for 3 flat threaded discs with no dimensions to work from. If I give him the circumference of the lens panel to go in the unipla at its widest point, it will be much cheaper.