I disagree wit the idea that threads weaken the monoblock, especially if the wall thickness is reasonable. Most bolt action rifles have their barrel threaded into the receiver, often with small rings and they are hardly weak. You can always use a finer thread as the threads won't be case hardened and they are better against vibration resistance anyway. (Most automotive thread are fine threads for that reason). As far as your difficulties with cutting threads and getting mounting faces and shoulders square, it all depends on the quality of your machinery and your level of skill. We cut a lot of threads at work, both external and internal with no problems at all, but then we are doing it a lot and have been doing them for a long time and we have good machinery and very good tooling which does make a difference.

Waidmannsheil.