This is just a sampling of the David Glen pictures on my hard drive. If you find a David Glen bagpipe, you'll most often find superb workmanship with excellent attention to detail.
You may find button mounts or projecting mounts. Some may have cut-beads and others may have round-beads. Some may be two-piece. All will be perfect! Note the stepped threaded tenon above. Very early Glen bagpipes had generous ivory ferrules atop very thin tenons. It takes a very steady and skilled hand to do this. Sometimes the tuning chambers were lined with a keyed brass insert. The bushing was generally flat, although a very modest bead can be found on some Glen pipes.
Early Glen 07
Early Glen 04
This very unusual David Glen set (above and below) sold on Ebay. The new owner contacted me soon thereafter and provided me with these pictures. I have no explanation for the ferrules. 
For me, the classic David Glen bagpipe is pictured below. Cocuswood. Button mounts with nickel ferrules and ivory rings and bushings. Easy on the shoulder. Exquisitely made and a joy to play. Although lower pitched, David Glen chanters are remarkably true.
David Glen