So I managed to buy a butt load of older train Mags at th;e local show a few weeks ago, and going through I found I had some issues of Railroad Modeler mags, and in "volume 4 No's 7" (July 1974) there is an excellent article on page 39 about a 2 in one layout (N and Z scales) by a chap called Steve Wright :) . He talks about how as each smaller scale came out, he converted his layouts down from H.O to TT, then scrapped the TT and went to N, and was now onto Z.
Some really neat model building, he has done some very clever rebuilds of the 0-6-0s into U.S style mallets 2-6-6-2's, the frames were cast from lead fishing sinkers poured into wooden molds! (lolz mad as a hatter anyone? ) and his freight cars are done on 4 truck car chassies with fake U.S side bolsters. His layout then also featured a heavily modified N scale turntable turned into Z, with auto indexing.
I really wish they had snapped a few more pictures, as he even scratch built his diesel frames back then. truely inspirational. I'm not sure of the copy write laws on this, considering the magazine is long out of print, but from searching the net I got no idea who to ask about it, although it seems a lot of modellers have been looking for articles out of it for years. keep an eye out for a copy.