Well done Chuck - And proof yet again that your average person can build, and maintain, one of these guns. Anybody can do this if they set their mind to it and aren't afraid to try.
A 20" bull barrel is a good choice. Should give you a real accurate shooter for 500 to 600 yards. Plenty of range to reach out and zap some Space Zombies.
Get yourself a good quality fore end, one that free floats the barrel, and some good optics, you should be set.....
Welcome to the SUR Family!