Hi Steve,
I think they can be changed over if the model and grade are the same. The escape wheel on your Elgin should fit right onto the arbor with a tiny bit of space left between the escape wheel and pinion rather than onto a shoulder cut into the pinion as found on the other train gears (If I’m wrong please let me know) which means you can measure the arbor diameters to make sure they are the same. There’s little danger in removing the escape wheel that you won’t be using and then testing the fit on the other arbor. Also if they do press onto and locate on the arbor then concentricity shouldn’t be a problem. The wheels that are fitted onto a turned shoulder on the pinion will sometimes not run true after changing them out but escape wheels are usually located on the arbor only.
I just re-read this and can see where what I said might be confusing. If so then please let me know and I’ll try to make it a little clearer.
Hope it’s helpful though.
Bob