Are the foldable ROPS and the fixed ROPs interchangeable? It looks like the ROPS subframe is welded to the tractor and the top portion is held on by four bolts. I would think that it would be a matter of taking out the four bolts and switching. Has anyone done this? I am looking at switching my foldable for a fixed ROPS and would more than likely get the fixed ROPS from the dealer and switch them myself. Thanks.