I am trying to determine if it makes sense to convert an M&P 15T to a SBR. I completely understand the NFA side of the equation and realize I need to file a Form 1. My question is what actually needs to be done to the rifle, new barrel and gas block? I realize that I will need to have the lower marked per BATF regulations as well. I also know I could simply buy a new upper. I am trying to determine if the conversion is less expensive but would still yield good results. Thanks in advance.