The best thing to do on any action is to use a pitch gage to determine the thread pitch and a depth mike to determine the bolt face to receiver face depth and the depth that the tenon needs to be cut depending upon how the bolt fits to the barrel, ie. coned bolt, counterbore, flat. Any measurements you need to make the tenon, you can get from the action. You can use a dial caliper or digital caliper to determine the thread diameter. I was looking at the Newlon print for the Shilen DGA and was surprised that the tenon diameter is listed at 1.075" as that isn't a standard thread, but they may have been where the castings cleaned up when they were cutting the receiver threads. But, you can also get the major diameter from the minor diameter measurement for the pitch of thread of the receiver with a little help from a Machinist's handbook.