I wouldn't touch it. There was a guy that tried to change one over and hack sawed the frame to fit motors in it. He just added 1 extra wheel to each axle of the pony wheels to get those to gauge. Then he spent years looking for the motors and gave up and sold it in horrible condition. He could not get the motors re-gauged, and ended up scraping them.
It's best to keep it and display it, or sell it and be patient for another to pop up for sale. There was one that sold on "that internet auction site" just a couple weeks ago. It was the rarer color scheme dark yellow & maroon, so the odds are in your favor for the next one will be in this color.
I really don't know why Rich-Art made them in G gauge!! It's a prewar toy train looking tinplate loco, and G gauge is scale for the most part. The only tinplate G gauge is the Marklin Maxi stuff. And I know someone will chime in that there was this gauge in the prewar tinplate era, like the big Marklin CER or HR66 locos and trains. I have a bunch of Marklin, Bing etc prewar gauge one trains. That is 3 rail, gauge 1 tinplate "toy train" track with tubular rails. The Rich-Art model I saw was made to run on the 2 rail G gauge, scale, plastic tie, "model train" track with solid rail. The gauge is the same for displaying train, but the trains do not interchange operationally.
The seller should have told you. That is why the low price. This reminds me of the time I bought a States car for $100 thinking that it was original because it had cast journal boxes. I bought it quick and moved on. When we got back to the car, I lifted the roof and realized that I bought a $75 (or less these days) Lion Lines kit car.
It will take a master craftsman to do the job right, and would be more than it's worth in cost. But even then, there are no motors available anywhere. I looked for a long time for the one I mentioned. So I would think real hard before I started taking it apart.