This maybe a stupid question, but Marty F helped me get a eccentric crank assembly for a Texas type from MTH.
Have you asked Marty for help?
Trainz had many extra MTH parts. Recently the listing has gone away? Maybe still, they would have it?
Any MTH part number I could help search for?
I lost the available part drawings when my computer went south. Urrggg.
My 2 larger old RK steam has the wheel part cast right in.