Need a JD 270 timing window for a CBC431-3AL pump

I have an old JD450() dozer with a CBC injector pump. I want to set/check the timing advance. The CBC pump is small, round and very obsolete. Most of these got changed out years ago. I have an identical pump in good condition as a backup. I need the small, round screw-in window to do the timing advance. It goes under Deere part number JD270 and Stanadyne part number 17180. This is the round window not the rectangular window on some of the later pumps. Anyone have an idea where I can get one. I Googled it until the tips of my finger bled. Does anyone know of a work around? Thanks John