My No4 rifle was bubba'd beyond redemption, so I went with a drill and tap weaver TO1 mount. I did the drilling and tapping myself so much cheaper, but even if you take it to a gunsmith, the total cost is about the same as the non-D&T mounts. As an added bonus, it also sits lower than most of the no drill mounts, giving a better cheek weld with an original military butt stock. If the gun is at all restorable though this is probably not the best way to go, as it will affect your resale value with the milsurp crowd.
BTW, I considered the angle iron mount idea from 303british.com, but in the end the Weaver mount was easier and cheaper in my oppinion. Lots of great stuff on that site though. Anybody shooting 303Brit should check it out.