Rich,
If you have ANY question about what you need to do, please ask FIRST. My explanations are not comprehensive by any stretch of the imagination. Please consider all the responses you get in addition to your reading to make sure you have as good an understanding of what needs to be done as possible.
Inletting locks and drilling for the bolt holes is difficult. There is one thing I didn't tell you about how I drill my lock bolt holes. Once I have the lock plate in the stock, I locate the position of the lock bolt holes inside the lock mortise. The rear bolt should be centered on the bolster inlet (assuming you have a nice tight inlet that accurately corresponds to the actual lock bolster) just behind the breech plug lug so that it will clear the lug. The front lock bolt should be centered on the wood in the lock mortise in front of the mainspring so that it clears the ramrod groove. Move the front bolt off center if you must to clear the ramrod hole.
Once you have located the bolt hole locations on the inside of the lock mortise, center punch those locations. Now, drill a hole through the stock from the inside of the lock mortise with the TAP DRILL. This way, you are certain that the bolts are in the correct location and you are ready to use the holes in the stock as guides to drill and tap the holes in the lock plate. If your stock is still reasonably square on both sides, a drill press is the best way to drill the holes through the stock. When you finish your lock panels they will slant in following the taper of the barrel. Because of this, the lock bolts will never be perfectly perpendicular to the lock panels. That is why I counterbore my side plate. It hides the fact that the lock bolt heads don't pull up flush with the plate.
Anyway, once the holes are drilled through the stock, you reinstall you lock, sans the cock and frizzen spring, and clamp it in the stock. Now you are going to use the holes you just drilled in the stock to drill the tap holes in the lock plate. Just drill from the side plate side with the appropriate tap drill through the lock plate. Now you are going to tap those holes using the lock bolt holes through the stock as a guide. Before you do that, though, you need to remove the lock and redrill the holes through the stock with the clearance drill so that the taps will go in easily. Once that is done, reinstall the lock and tap the holes in the lockplate using the bolt holes through the stock. You may be only able to get the holes started before your tap wrench hits up against the stock. In that case, just remove the lock to finish tapping the holes.
This is the most fool proof method I know for drilling lock bolt holes. You will reverse this process for locating and drilling the side plate holes. Only, in that case, you drill the rear lock bolt hole in the side plate blank, put a bolt though that hole into the stock to set that location, clamp the side plate blank to the stock covering the front bolt hole and then drill that hole through the side plate bank from the inside of the lock mortise. Once you have the holes drilled in the correct location in the side plate blank, you can finish filing it to shape.
I hope this makes things a bit clearer for you.
Don't forget to look at the tutorials and check the archives before you start a task to see if there is any additional help or advice available.
Mark E.
