Lowers are available and fairly inexpensive today. Why not build up one you like and sell the Stag lower?
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek
I went to Anderson's website and they say that it does not come with a jig. They do not offer a jig either. One of the reasons (besides money) I don't have an 80% lower is because the jigs are so costly.