The Pacific Tool unit is a very nicely made bolt shroud and safety which does require a substantial amount of fitting.
The safety and bolt lock are similar to that employed on the M70 but the bolt sleeve lock is somewhat different as it consists of a plunger and detent rather than being an actual "lock".
By the way, for those unfamiliar, the bolt sleeve lock serves to keep the bolt shroud from rotating when the safety lever is in the intermediate position and the bolt is open. In this position the nose of the cocking piece is lifted out of the notch in the rear of the bolt body so the whole works could rotate when the bolt was open. The lock or, in this case, the detent, prevents this.
Dennis,
Some people just like things for no good reason and others like them because they've had a bunch of gunwriters telling them for years that a given system was the ULTIMATE in rifle design. I put one on a mauser actioned rifle I use just so it would be the same as the half dozen model seventies I use. My thinking was that I would be less likely to screw up under pressure if all the rifles were similar. Sadly, regardless of the type of safety on the rifle, a klutz is still a klutz and likely to forget to flip the thing off before trying to shoot that really big bull! Regards, Bill.