If I am understanding you, the lock you want to use is already drilled for the lock bolts.
If that is the case, I think I would wait till I had the parts in hand, the barrel inlet, and the ramrod hole drilled. Then I would align the lock and trigger guard where I want them to go on the stock and see if the holes can be used as is. My gut instinct is that you will probably end up having to weld them up because the location of these holes is pretty "touchy" and dependent on lots of variables.
For instance, the gun I am doing now has a very thin web under the barrel near the lock, AND it is one of Chamber's Early Germanic locks that can be hard to align "just right", AND these locks also have a very small area for the front lock bolt. So, set the lock where it looks architecturally right, and to keep the bolt from blocking the ramrod hole, I am moving the bolt up above the centerline of the lock to make all the parts play nice in that cramped area.