Interesting idea... the main hurdle I would see is the fact that whilst you could find an old 28mm stanchion double crown assembly, Manitou had changed their approach to bushings from Manitou4 to Mach5 so the bushings interface between a newer dual crown upper stanchion assembly and the old Manitou 3 lowers wouldn't be compatible. Also the distance between the legs (center to center) wouldn't be compatible which would mean at the very least you would need to have custom upper braces machined. In theory possible, but a lot of tinkering and custom machining necessary (probably not worth it in the grand scheme of things).