With the variation of track gauges and where never the twain shall meet ... perhaps a layout based along the lines of DKBM in Northern Germany would be a good idea ... Gn15, Feldbahn and IIe running on the same track ???? Surely it wouldn't be prototypical ????
The real Nicky & Frank S (as modelled by LGB), has, (since the RüKB almost went bust) been re-gauged to 600mm and is now on the DKBM (Dampf KleinBahn Museum) at Gütersloh. At present it is still outwardly recognisable as N&FS but may later be re-painted into wartime grey and revert to it's original number "4" (which was the loco that became Frank S in preservation). Originally Herr W. Seidensticker owned two of these locos and named them after his two sons. When the boiler on Nicky S failed, one good loco was made from the two, named Nicky & Frank S and used on the RüKB on the Baltic island of Rügen. A non working example was made up from all the worst parts and (Nicky S) is now on a plinthed display in a military museum at Ingolstadt.
Although the working N&FS has found a new home, its route is now a contrived circle that is more like a park miniature line ... (or a giant garden railway !!! ... see pic) The roles have reversed, the real loco now mimics the model. In good hands perhaps but this is like a retirement home for old locos IMO.
http://www.dampfkleinbahn.de/