My project this last week was to retrofit an Athearn SDP40F chassis from the standard blue box drive to hex drive. It now sports a new motor and flywheels, screwdown motor mounts, hex shafts, delrin worms and nickel silver wheels. It now runs as quite and smooth as any of my Proto 2000 and Atlas locos.
This is before the retrofit:
And after the retrofit:
The contact strip will be removed later when I install a DCC decoder.
This is before the retrofit:

And after the retrofit:

The contact strip will be removed later when I install a DCC decoder.