I was sorta involved in 7-1/2 gauge (1-1/2 scale) for a while. Then life kept getting in the way and I am no longer physically able to pursue the idea. I had intended to use real rail at some locations and 3/4 angle for most of the rest. Instead of casting wheels, I intended to use disk brake rotors from small automobiles and cut off the disk, leaving just enough for a flange. The hubs I actually started with were of many sizes, I was going to pair them up to make wheelsets. Cast aluminium cores with steel bands would be a fairly solid substitute.
What you are conceiving will be a larger gauge, 12-15 inches. And only remotely scaled. I would say that with iron wheels, you could easily use 1-1/4 or 1-1/2 angle iron for track. Switches, turnouts, can be easily fabricated from angle iron, especially for 4 wheel cars. 2 X 4 crossties on 10-12 inch centers, ~30 inches long. Pressure treated of course.
There are many web sites on the subject, mostly for semi-scale 1/8 scale, 1-1/2 "/ft, 7-1/4 " gauge. I don't have the links handy, but you could spend days prowling around to find something in your area of interest. I am partial to electric propulsion, steam is dangerous and a hobby in itself. Gasoline driven electrics are not as common but definately a viable system.
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