So I got this used complete upper very cheap. I just bought a $50 Bear Creek stainless barrel on sale to replace the original shot out barrel. I just hit a speed bump getting started on the swap. The old barrel has two slots for the pins and the new barrel looks to have a detent for a set screw. It is a fixed carry handle upper so want to stick with the original style sights. Here are pics of what I am working with.
Thanks for the help.