Hopefully I can avoid muddying the waters further. Agalb is mistaken, I believe, with a DIAS you can have all those evil nasty features prohibited by the 94 ban as it exempted machine guns. I asked about this a few years ago, I was hoping it exempted all NFA guns. I was thinking of building a semi auto M4 but the Technical Branch of the BATF said their interpretation would only exempt machine guns not SBRs. You may want to talk to the tech folks at BATF before you sink a few thousand into a sear that they won't allow you to use as you want. Actually I would talk to a competent smith who has experience with NFA guns to see if it is practical before you do anything else, the Technology Branch will ask questions about how you intend to do the conversion to see if it will fit within their guidlines.
Did that help?