The very first time when I tried to mount 6” HV RT vertically, I observed that this rotary table is not designed for my mill cross table. T-slot grooves on my mill (HF40939) table are not suitable for this rotary table. Didn’t want to secure rotary table by clamps as there is no enough space to do it properly, so it was required to drill and tap holes in mill table and secure RT with double end studs. Drilled 2 holes 119.5 mm apart and threaded them with M10 thread. Two socket set screws serve as plugs to prevent chips filling when rotary table is not in use. Looks like this RT is designed for some bigger mill as aligning keys are 16 mm wide and grooves at my mill table are 13.8 mm wide. Milling of these keys to 13.8 mm was done first.
Hope this info can help.