Take that sks to a gunsmith. Its a sharp lookin rig, def worth fixing it.
@matt,
have you tried a bunch of different ammo? My 1944 Enfield .303 would 'key-hole' (buttets hit sideways) out to 100yds then I couldn't find hits at 100yds while using cheap ammo (PPU Partizan russian made). Then I used S&B and it worked great, no key hole, 4" high at 100yds. I measured the bullets and found the PPU dia. was .308 and the S&B was .311 The .303 Brit is suppose to be .311. Just saying, not all .30cal manufacturers do the same thing.
have you tried zeroing at a shorter range and walking it out? Theres no sense in "fixing" it if you can tight group at 25 or 50yards. But if you can't keep a group at short range its possible the barrel is shot out.