To do a thorough job of removing Suncorite, preparing the metal for a proper reblue, and then hot bluing would be a fine example of investing time and money in a project that would result in a rifle worth less than before you started. It would certainly result in one less collectable No.4 Mk.2 rifle. Some of these 1950s ex-British War Reserve rifles are in rather fine condition.
Suncorite is toxic prior to application. No idea what its cured dust is like, from an inhalation standpoint.