Thank You Marvin,
The 1976 Glenfield 20/Model 80G appears to be my safety mechanism. I have installed it correctly according to the photo. However, the rifle will fire in either the Safe or Fire position. I am going to purchase another from "Numrich" and install it to rule out a worn part. It looks to be fine to the eye, but sometimes that means nothing.
I SINCERELY appreciate your follow up and I apologize for the mistake of posting the incorrect model cross reference. My rifle is a Sears and Roebuck 43-103-2850 SL&LR. This may be helpful to anyone else who has this rifle with a similar issue.