Hey David,
it was surely for a good reason that they offered a third “stiffy” rail for the 35 mm rails on X axis on Woodworker and when relasing Journeyman they offer the new X rail for 48″ workarea width only with rails of 50 mm diameter. Therefore I would assume for having 48″ workarea depth too, you should have Y-50 rails.
I don’t know if they are stainless steel, surely they are chrome-plated, induction-hardened steel, probably 52100 Bearing Steel Equivalent
I don’t know whether the manufacturer @OnefinityCNC reveals/revealed which material/hardness they chose?
Bill wrote that on X-35 the dimensions are
Anyway if you are not able to do the machining of the feet yourself, and the manufacturer doesn’t sell you the parts you want, you can only purchase the 35 mm hollow shafts which, as I said, I believe for good reasons were not used when increasing the length for Journeyman’s 48″ workarea width.