The GS-4 uses Boxpoc drivers.  At the time, the only source I could find was from "Little Engines".  These drivers were very well made but were not exactly like the GS-4.  Oh well!  This was my first attempt at machining cast iron.  I burnt quite a few brain cells trying to figure out where/how to start machining them.  I looked at several articles and decided it's time to bite the bullet.   The centers were drilled, bored and then reamed.  I then mounted them in the lathe and began cutting.  

I did the backside first, then turned them around and did the front.  I saved the tire and flanges for last.  I must be lucky because everything turned out fine.  I also had to make "custom" cutters for my lathe to get the proper profile (another learning experience).  After completing all 8 of them, it was time to look at my work and be amazed I didn't screw up.