I should have added that Q Gauge is 1 3/16", or slightly narrower than our O Gauge track. It, too, is not correct for O Scale, but Proto-48 is indeed correct.
I started with 1 1/8" gauge in 1957, not knowing about Q gauge. My thought was that our treads were too wide, and I wanted side frames and main rods to be where they should be, with respect to the car bodies and drivers.
I still have a loop of 1 1/8" gauge. Looks a lot better than our wide gauge with most O Scale models. I now prefer the massive look of 17/64 models.
I will get you a photo or two of 17/64 Scale locomotives in a minute.
This one was my third attempt. Main frames were extended Challenger frames, cylinder blocks were hogged out of solid brass, and tender trucks were cast from my patterns in proper 17/64 scale. Power is Pittman/NWSL.
This one is the big Baldwin 3- cylinder compound. Its prototype resides in The Franklin Museum in Philadelphia. The proper tender is here as well; this photo shows an SP tender, which was actually used during trials eastbound in the Sierras. The locomotive had been converted to oil temporarily, and they did not convert the tender. Enthusiasts found gold lettering under many layers of black on a 120 C tender like this one.
I have about 20 such models around here - probably more 17/64 Scale locomotives than anyone else on the planet except maybe Carey Williams. I also have maybe ten kit-built and imported 17/64 Scale locomotives, and a bunch of matching cars.