For bolt timeing... you need to talk to these guys... http://www.sharpshootersupply.com/
The recoil lug is frequently upgraded from the stock for a couple of reasons... on the larger calibers, thew will eventually bend a bit. Further, the factory recoil lug is a stamped item... and as a result is frequently bit thicker at the top or bottom.
Aftermarket items are almost universally thicker, and machined.
As for my suggestion of altering headspace to fit your ammo... if youre only shoting one kind, this could pay off. Ive done it on a few 308s that were a bit long, and 2 300WMs that were way off... and all shot better, and gave better brass life. A definate positive when (not if) you eventually start reloading.