Sadly nothing with that serial number turns up between December 1977 and April 1983 which leads me to think it could be a late one Geoff produced in 1984...or possibly slightly later??

It's difficult to believe Geoff was still producing No.4 conversions as late the 1980's given the Swing came out in 1971 and started to immediately dominate the target rifle scene; what's that old saying...you can't keep a good rifle down!