There are 3 types of "80%" AR lowers, depending on which portion is left unfinished: the magazine well, the fire control group recess, or the threaded hole for the buffer tube. (If I were to mess with one of these, I would pick the second type.)
It seems it would be easier just to get a finished lower.
Some people like to work on these as a hobby challenge, but I suspect that more people go that route just to fly under the radar. I'm not that paranoid (yet).