wedge,
I was not aware the 66 red eyes were made with reverse. As far as I know the reverse / back tacking feature came along after the red eyes were discontinued. There was an after market retro fit kit for them made around WWII. This looks like a little plate with a lever that comes around it from the back side.
The 66s with reverse came along in the 40s "I think". Any chance of you posting a pic of your machine?
That was a good buy for it.
Joe