Well the winds of luck blew in my direction. I went by a buddies house to look at his new Colt 6940...nice gun!! I made mention that I was going to have to buy the upper assembly vise block to change out to my new A4 upper I had recently purchased, and he went and got one out of his tool chest along with a multi tool, which I already had. Using the block was the way to go and it took all of about one hour to make the switch. Everything went into place perfectly and I was just amazed. Now I have a more versitle gun gor home defense and just fun shooting. I think I will keep the A1 upper for a future retro build I am thinking of...who knows??? Here is the finished product and everything I want to do to this little Bushmaster except finding a rear folding sight.