My '74 LPC came with a lightweight stop bar... problem is, it has threaded holes a la wrap around (no inset screws). I acquired it 42 years after production, and I don't know all of its stories. But, there you go.
My current '71 LP Deluxe has an aluminum tailpiece.
When I bought my earlier '73, however, it had a non-original something or another tailpiece. I'm not sure what it was, but it certainly didn't come from Gibson. As luck would have it, one of the local music stores had a bin full of used parts and I was able to grab a period correct aluminum and a later steel tailpiece.
I tried them both (using the same style/gauge strings) and to my ears the two tailpieces sounded very close to the same. That is to say, neither I nor my bandmates could distinguish any difference.
I will say that the non-original tailpiece that came with the guitar sounded dull and flat when compared to the Gibsons. It didn't have as much sustain and didn't allow the voice of the guitar to come through as well.