Pete, the button side goes up, the tang down through the slot. The 1st one of these I did it took me an hour to figure it out, now I can do it in 5 minutes.
If you bought one from Wayne, there is no part #770, as he makes his out of heavier material and it is not necessary. Wayne also includes a teflon washer to make it slide easier. I also use a little grease on the slide.
Good Luck!