I've got a couple of those units, smaller version. The axle only protrudes into the wheels about half the width of the wheel hub. So the wheel hub gets hogged out and "droops". A conventional wheel will have no way to attach on the short axle, The plastic wheels are held on by a 1/4" (?) bolt across the diameter of the shaft. Conventional wheels are pinned on the outside of the hub. I haven't found a quick EZ replacement yet... but now I have a few of those units, so I'll hafta devise something.... Like a longer axle. And parts machines of that vintage all seem to have the same wear...... on the units I've seen.
GLuck, Jay