I've posted this elsewhere (but don't remember exactly where

ops: ) so I'll offer it again. While this won't give you the RP25 tread profile, there is an easy way to turn down the flanges on locos like those from IHC. All you need is a pair of leads from your power pack and a cut-off disk in your Dremel.
If you keep the loco upright, you probably won't even have to disassemble it, beyond taking the body off to get at the motor. Clip the leads to the motor, then turn on the power, holding the loco upright in your hand. Get the wheels turning at about half-speed. With the Dremel running at high speed,
lightly touch the face (
not the edge) of the cut-off disk to a wheel flange, keeping the point of contact as low as possible to avoid getting the cutting residue in the mechanism of the loco. The light touch is very important, both to avoid shattering the disk, and also to avoid overheating the tire of the wheel, as the driver centres are plastic. Work for a few seconds on one driver, then go to another, alternating until you get them all to the stage you need for operation on your track. If you think that you may have gotten any cutting residue in the mechanism, disassemble the loco and clean it thoroughly. It's been some time since I did mine and I vaguely recall protecting some areas with masking tape, although I'd have to take it apart to elaborate on that.
You can try turning the unpowered wheels by hand, but a better solution is to remove them, then chuck them in a drill to get them turning at a higher speed. You could also replace them with more suitable wheels.
Wayne