This comes up every so often. The most authoritative thing I have seen said there was no problem. IIRC, the ATF doesn’t consider it to be constructive intent to have both a receiver and FA parts as long as the third hole is not drilled. When it comes to constructive intent, they are concerned about things like AR15 FA drop in sears that allow you to readily convert the rifle. Interpretation of the word readily is the tipping point. If you had the FA parts, a FA template and the correct size drill bit stored together in a drawer, that would certainly look very bad. If you have that bad stuff and you are the kind of guy that makes his neighbors or the local LE nervous, you are definitely at risk. If you have the FA parts and there isn’t any sign that you intend to use them, and you are an upstanding citizen, there really shouldn’t be any risk. I happen keep mine for investment reasons only. Who knows what they will be worth some day. For the record, I have no intent to use them as long as it is illegal. I have way too much to loose. But hey, this is an individual decision. And, for all you know, I am some fiendish ATF guy trying to lure people into confessing that they keep their FA parts.