Mystery to me Bruce, that adapter does not seem to match either the old FT adapter or the new one for the M90.It looks more like the original WO 'foot' adapter with the Ft focuser screwed directly into it.
If you have a look at this
http://www.williamoptics.com/support...d/megrez90.pdf you will note that the adapter that screws onto the telescope tube is the same as yours but the focuser is actually about 30mm shorter overall so unless the drawtube in yours is 30 mm longer than the stock focuser you will need an extension tube. I don't know how the previous owner used it like that unless he had either binoviewers or extn tubes.
Good luck!