You don't have to disassemble the lock for inletting. You can if you are more comfortable doing that, but it is quicker and you get a better inlet by inletting the lock assembled. You just have to be very careful about where you drill the hole for the sear arm. To get started that way, you position the lock about where you want it and mark the position of the sear arm on the stock. Do this two or three times to make sure that it is right. Then drill a 3/8" (double check that this is not going to be too big for your lock plate before you drill) hole 60% of the way through the stock with the sear bar resting at the bottom of the hole. Once this is done you mark all the internal surfaces of the lock with a large, permanent magic marker as the transfer agent. Then it is just the a matter of fitting the lock, tapping with a mallet, and removing the black wood. Once your screws and the tumbler pivot point are marked you are safe to remove th appropriate diameter of wood down and 1/8" to 1/4". You can also safely remove 1/4" of wood where the spring is going. Also, cut out the area of the bolster where it intersects the barrel channel using a small backsaw and a chisel ( leave the little strip of wood between the bolster and spring, if you can). All this will speed up the inletting process.
Once you have the lock plate sitting flat on the stock in the right position, you can trace around it with a sharp pencil and the real fun begins. The inletting will be a bit slower from this point as you remove just the high spots. It is best to stamp in the outline of the lock plate. You stamp just inside the pencil line. You should use a small stamping chisel to do this. Mine is made out of a 6" piece of 3/32" music wire. You grind the tip(1/8") into a convex lens shape that tapers to a chisel point. The convex shape pushes the wood away making it easier to turn a corner. You walk the stamper forward, overlaping the last cut by a third and tapping with a small hammer two or three light taps. It should go in about a 1/16".
You will also need a 1/4" bench chisel, a 5mm #1 skew, a 5mm dogleg chisel, and a 5mm #9 at the very least.
With all of this, until you have the plate in the stock, double check the position of the lock before you make a cut .
