well, the BR-52 from JTFM is 1/56 but the running gear fits onto 1/60th track (S scale), the problem may not be the size difference of the two pieces but that the 1/48 running gear is in O scale. The BR-52 is one of the greatest kits for 28mm ever made, even if I do say so myself
As for railguns, well it's been discussed and may be a future project 1-2 years, but it's still only a possibility.
There are 1/48 railguns available from a French firm (but the name escapes me at the mo' , the sell Solido), and they are VERY expensive.