I can't put my fingers on it, but in either one of Ehrenburger's or Dorman's books is a very short coorespondence between the Fuller and West/Perlman asking if the DRGW was interested in taking over any part of the RGS.
The answer was a very clear..... "no".
I've also been trying to find my motive power folios without luck (hate it when I clean things up). It seems to me a K28 is quite a bit heavier. They have a longer rigid wheelbase and much longer total wheelbase. A K28 tender wieghs almost as much as a K36 tank. If the RGS sidelined 455's cut down SG tank because it was too big and topheavy, a 49 ton K28 tank would have been a disaster.
Perhaps at one time portions of the RGS could have supported a K28, but certainly not in the last several years of its existance.