Hi Trevor,
It's best you contact FX Distribution UK direct and ask, things have changed over time and serial numbers can give a track and trace to what model you have and what may need changing.
Retail Sales:
Phone: +44 01392 354854
info@sportsmanguncentre.com
http://www.sportsmanguncentre.com
I would phone - email can take time. They have a specialist and can advise.
I also have to be careful advising on a public forum how / what to upgrade to change a rifle.
Sportsman can give you the best idea.
Cheers
G