I bought this Sovereign 1 years back and actually used it for a while. It came with the stock Sovereign frame but I’ve since switched on a Bob Long 45 frame that has been modified for the Sovereign Switch.
Based on the other parts on the Sovereign the Bob Long Frame came off I would guess the frame was cut for the Sovereign 1 switch by John Gross from Florida Paintball Center.
This Sterling Sovereign 1 was originally modified (reg added and a few other minor details) by Terry and Jeremy Garrett at G3PB. They also had it anodized in the British Racing Green. I have a matched LPR, trigger shoe, barrel and stock for it somewhere.
It is also pictured with an Eclipse Ram bolt. original Sovereign 1 is c . 1996-1997 from the UK and modifications by G3PB were likely around 1999-2001.
Find the pictured modifications on the archived G3PB website at http://web.archive.org/web/20020121150104/http://g3pb.com/
And more articles on Sovereigns at https://paintballhistory.com/tag/sovereign