While I'm thinking about it...if you go rifle gas with a flip up gas block and the 12" tube, it doesn't really matter if the PRI rail is 1/16" too tall since the sight isn't mounted on it. You could still get the SPR sleeve for continuity, or even just buy the PRI tube that comes without the rail sections and save a few bucks. Just comes down to what you want the end result to look like.
Damn, I sound like PRI is paying me for this sales pitch!