I did some reading. IMO using a good 56% silver solder paste and some heat stopping paste is probably the best method. I've seen a few pin/welds fail easily.
Working on a pretty elaborate thread protector for an ops inc 3rd model barrel profile all day. Probably have about 5 hours in it so far. Could reproduce it much faster but it has been a very interesting project so far. If I was going to produce it it would be two parts tigged together. 5" deep bore is not fun for me. I need a beefier boring bar. Started life as 304 round bar. Tubing would be the way to go welding the threaded piece in the end.
Look into a reamer set =)