It looks like a very nice build to me. I've packed the space between my mixing tube and burner mount with kaowool, rigidized it so no air can go that way. also, I started with one row of burner mounting bolts and after one mishap realized I needed a second row which I installed. the second set of mounting bolts really secures the burner rigid. Also, I think it was Frosty who alerted me to the chimney effect the burner has when the forge is just shut down. I have a choke cap that I routinely close right after forging to keep the air flow and heating of the jet tube to a minimum from super heated air rushing back up the burner. Don't know if this is critical, but It is part of my routine.
Nice work