Damon - I've got a post-ban (produced within the last year) Bushy lower. I think if I sand the .04 down any more, the stock will protrude too far into the lower, and completely block the detent pin from coming up. I suspect if I can get a .03, i can probably mix&match to get .07 or .08, which might work better. failing that, the .04 plus the 180-threaded tube would work well too.
NightOwl - yeah, I know theres a 180 tube available; that'd probably work too, but first I need to actually speak to someone at magpul. No luck there, and I can't afford to call over and over from work. I'm hoping to catch his attention either here, or with email. I'll resend the note I sent him last week, I guess.