OK, I'm going to go out on a limb here. I'm new to this, too, but I think you are where I was a month or so ago. I was told to mark the location of the touchhole/vent liner, but DON'T drill it untill the lock is morticed in. The rear lock bolt is supposed to go through the breech plug tang. I was told to line the rear of the lock up with the center of the wrist of the stock, taking into consideration the relationship of the pan and the touch hole. What I didn't know was the lock panel itself should be parallel with the bottom of the stock.
I practiced inletting the lock on a scrap. Actually I made a scrap stock to practice everything on. Be careful about locating your front lock bolt- especially if you have removed your mainspring.