Can't think of the base name as I write but I have that base at home and will look later. It was on a model 70 I have. It was the flip off type mount that you roll to the left so you can use the open sights. Not very fancy and unfortunately detracts significant from the value. I would estimate as much as 20 to 25%. I'll let you know the name later.
Just thinking it may be a pachmayr.