I'm looking at picking up a good used 1975 BT99 for my son to shoot trap with. It is a good price but is a fixed full choke barrel. I'm planning on a Precision Fix stock so it will fit and grow with him. I'm also looking at a new threaded barrel with choke tubes so he can use it from all distances. On the website for the barrel it stated that it will need fitting and head space stuff. How hard is that to do? I just want to be sure I don't end up with a $500-600 barrel that I can't do anything with. Thanks all.