I don't know about the 80% AR's but a guy I know did a 80% "Razor" 10/22 magnum and it turned out very well. Took some time and a quality drill press to finish. It actually functions 100% of the time, which is WAY better than the actual Ruger WMR ever did. Also, the way the 10/22 magnums are priced right now, his was cheaper to build.
I would imagine that the AR would be harder build to complete though as every one I've looked at would take a milling machine to actually finish.