I'd go pinned/welded.
I've got uppers in 14.5" and 14.7". Both are pinned/welded to 16". I've also got pistol uppers and a braced pistol lower.
Kind of nice to put a real buttstock on the 14.X" uppers.
Agree. I have 2 14.5 barrels with a pinned flash hider. I want to build a 12.5" with some kind of extended flash hider for my next one. I think 12.5 is short enough. I see no value in 5.56 pistols and I don't want to mess around getting the short barreled rifle federal permit.
kwg