Recently I came across a review of the Beseler/Ross unit written (by Jock Sturges no less) when it was still a Ross, not a Beseler. The way the original prototype was described it sounded easy enough for someone with my limted skills to tackle. I had intended to use wood and parts from an old Elwood when I got around to it. Maybe that's just good writing though. The article did mention that you had to use a 210mm.
The Ross model did intend you take the enlarger head apart - easier on older ones as they have sliding "Graflock" type clamps for each section.
I should think you could get a parts list/schematic from Beseler directly. Maybe contact Alan Ross at www.alanrossphotography.com