So maybe it was not a sporter rebuilt and put together by someone from parts in his garage and it could possibly be a BSA factory refitted rifle done post war for some reason unknown now? The serial number font on the barrel is exactly the same as the font stamped on the bolt and nose cap!
Also post war bayonets when rebuilt were given a blued all over finish, including the blade, they found it was not good to let the enemy know you were about to go over the top by flashing your shiny blades at them first. When I was in the army all of our bayonets had dark finished blades except the parade ones.