I built one of theirs last year. Same thing. I had to fool with the fit and finish just a bit, with files, but it came out fine in the end. That's for the hooked breech joint.
As far as drilling the hole, yes its right. Made me nervous, but the breech plug is not flat faced. Its drilled hollow. Those are the ones they Xray for safety. Was very happy after I looked it all over with a bore scope. You can run a stiff wire down the barrel and into the plug, then mark the outside depth with pencil. You will sleep better before drilling it.
Be very cautious getting the trigger guard in place. That was the hardest part of the build.