They used to cut them with a band saw which made welding so much easier. Then several years ago, ATF changed the receiver destruction requirement to three torch cuts removing 1/4" of metal each in the process making life much more difficult. After 1968 until May 1986, many cut Brens were rewelded into fully functional registered LMG's. I'd guess the majority were done in the 1980's when the kits became available in quantity. The double dovetail 1940 date gun that we changed the gas cylinder on several years ago was one of those. The phosphate and baked Suncorite 259 refinish made it look much better than it ever had although if you looked real close you could see where the welds weren't perfect. It hasn't changed the function though. It runs like a new gun at my friend's place in Virginia. I'll never forget that job. The long distance Armourer's course, unscrewing the original gas cylinder while my partner Craig held the huge torch on it and keeping it cherry red hot gave me a pucker factor of 12! If those fine threads had galled in my friends $25,000 gun, I hate to think of fixing that. Welding in a sleeve and rethreading etc, etc, etc.