No no, I understand. I bought my Lightning Link for $350 a long time ago, it was all I could afford and it's run fine.
I was just saying go slow regardless of what you do, wouldn't want to get bit with this much money on the line
As for the parts you are correct. If you take out the RLL or RDIAS, the gun no longer can be SBR as well. You can still own the upper, just not have it attached to any lowers. Used to be a fear of "constructive intent" but the Thompson Contender case pretty much settled that.
I have an AR also registered as an SBR since I don't want to fool with all of it, but you are right in your understanding. It can get confusing.
The next question is would you really move it around that much? Hard to tell. If you're into multiple calibers you very well might.
The receiver itself is the important part with a RR M16 (or conversion, there were some Ar's drilled to be the same as an M16). Every part in there you can replace or have worked on except the receiver itself. Some of the sear pin holes wallow out and get sloppy, hard to fix. Rare but it happens. As for repairs I've heard of people having receivers re-welded but I don't know what success rate there is for that.
I suppose you could break an RDIAS too, dunno much about those.
With my RLL you break or bend the paddle end pretty regularly, but that's not the piece with the serial number so it's easily replaced.
Lots of cash laying out there!