So the foresight is at 12:05 when viewed from the front? (or 11:55 when viewed from the rear...)
Trouble is, its very difficult to shim such a small error - the shim has to be very thin to correct 5-10o, and they usually tear or crush when being torqued up.
(in service, the armourer would try several barrels until he found one that went hand-tight about 20o from vertical, which gave about the correct torque to final index).
Whereabouts are you? I'd normally take a rifle like that to Terry Abrams in Essex, who has the correct barrel chocks and action vise to adjust the barrel. If your barrel is fairly decent, it would probably be worth p-exing it for a new barrel that fits correctly. There are plenty of new SMLE barrels about at the moment, so its not so expensive.