Just a heads up, when I did one a few years back, part of the pending research process included a request from the NFA examiner to clearly describe what I was starting with, preferably a photograph. I had noted in my original description that I was intending to use said 80% lower and that I would be applying markings as part of my work. SO...I sent them a couple of photos of the unmachined and unmarked 80% lower. Everything went right through after the photos were sent.
The retro AR15 world was going through some turmoil around this same time for 80% lowers having been sent to an anodizing shop with colt retro markings already done [to include an off position and oversized fake 3rd pin marking above the selector] and I think that may have contributed to the requests for photos.
Good luck.