B Smith - yeah, seems about right. My "Q"gauge is 1 1/8" gauge, or 4'6". My wheels are .172 tread, which puts the outside of the wheel (and side frame) at just about exactly the right spot. I have four locomotives and maybe eight cars converted to that gauge. It was just too much work.
The 17/64 models are larger, which makes me happy in several ways. Plus, they can be run on others' railroads if clearances are not too tight.