they hog out the areas such as the lock mortise, barrel channel, and trigger with a template and a router, you have to do the final fit
I bought my first longrifle kit from Wayne Dunlap. I would say those parts were pre inlet although not to the extent of a Lyman GPR. The inletting for
all the brass furniture was hogged out, as you say, but to such a close tolerance that very little work was needed for a good fit. Of course the breech area and tang needed considerable work and I spent plenty of time on the butt plate to make the best fit. I changed the trigger to a double set trigger so that obviously required more work. I don't recall having to do much on the lock..
Even on an in-the-white rifle I bought from Tip Curtis I put more time into the butt plate and toe plate for a better finish. And I worked on the lock mortise to get the best match up with the barrel.
My Sitting Fox kit was only preinlet for the barrel and ramrod, but I chose that option.
I guess what I'm trying to tell shademtman is to shop around and talk to the dealers. Most of the suppliers will do eveything possible to accomodate you.
If you buy a Lyman or Pedersoli kit for example, you'll be dealing with a distributor.
Salt