I too have similar problems s with a fixed and a moving steady for my Sphere / Atlas . I purchased the set off eBay and think I can modify /set things up reasonably accurately & easily enough ,
For the fixed steady I'm thinking of turning two identical top hats with two 12 mm tapped holes in one of them , two precision clearance holes in the other for precision shouldered high tensile steel bolts ( upper one the rim sitting on ways with at least 1" of brim on the ways for the above the way part . The " stove pipe" of the top hats will fit precisely in between the parallel faces of the ways , when clamped up there will be about 1.5 thou clearance between the top faces of the top hats . I think I may have to have conical precision locating pegs as well so that it can be set up easily every time at right angles to the travel axis of the saddle
The underside being the same wide brim . The rim of the brim of the underside hat will be cut on opposite sides of the perimeter and finished off in the four jaw to get square faces so that I can slip in between the ways by turning it side ways a tad then turning it back , putting the widest edge across the ways to get a decent length of shoulder on the ways .
The travelling steady .. It looks like I will have to carefully work out where it's minimum jaw / centre line is and then precisely drill & tap the saddle to fit it vertically with two precision shouldered bolts to locate it .... It may be best to set a long turned bar between centers & set things up using the turned bar in situ as the guide / accurate positioning device ...providing the bronze/brass legs of the rests are all equally set to the same length ( using calipers ) .