Back in the day, we didn't have a ton of choices. B-Square made the first one piece mount that I could afford and it was so flimsy it looked like it was about to break in the package. A.R.M.S. made the swan sleeve that incorporated a BUIS and you could use any rings to suit your need. I also used an ARMS #5 riser that was similar but no BUIS.
ARMS also had this aluminum skeleton that weighed almost as much as the gun, it was basically a rail but it attached to the upper's Picatinny rail.
We've come a long ways in 20 years or so.
