The perfected modification of Boer war era Lee Enfield rifles to charger-loading status involved the retrofitting of a charger guide and the use of a modified magazine to feed Mk VII ammunition. USMC scout sniper rifles are fitted with a one piece scope mounting base which includes a charger guide and this might be the best way to go because it would simplify alignment work. If you speak nicely to your local (genuine) gunsmith, and avoid discussion of finishing times, you might be able to get it as a QD item (either as a scratchbuilt project or modification of proprietary kit).
Best of luck.