Ok i got your pk3 file renamed the tik file in it to sprinfield and it kinda worked. The sound isnt right,it loads like a m1 garand, you have to scroll through your weapons to bring it up instead of it equipping you from the start when u spawn, and the weapon select screen for the british is the one from breakthrough. The modified version is here
http://dle1977.tripod.com/User-EnfieldSniperMod.pk3
screenshots
http://dle1977.tripod.com/shot0014.jpg
http://dle1977.tripod.com/shot0015.jpg
http://dle1977.tripod.com/shot0016.jpg
All i can tell u is to experiment with the files i think it is possible to do, hope this helps u on your experiment
oh yea it was SH Untersiete i tried it on btw