I don't know what insert you have in mind but there used to be one for the 30 cal to make it 7.62x51. I had an M1icon I converted, used sleeve locker inside a cleaned and degreased chamber and then ran a ream in so it headspaced correctly on a go gauge. The insert was supposed to be removable but I didn't want that. I never had any failures and as hard as I'd try it didn't shoot loose. I'd go through clip after clip and it stayed put until I sold it. The chamber was changed though, would have a ring where the shoulder of the 7.62 came up. I'd expect you might see something similar. I think it could be done. The mags, I wouldn't worry about unless you have stoppages.