Dave wrote....
 ... OR a token ring option board and cable set for a
3174-51R. 
I got my token ring option board from 
lordsnet.com. I told the guy what
all
I was doing, and he gave me "hobbyist pricing". I think he also included a
set of version C microcode disks, as that version is required for
reverse3270. I think I also picked up a second floppy drive and maybe some
memory from him - so I could run version C.
J