An RSA, VTAC LPSM, or Fortis QD, or the standard DD/GearSector/KAC Side QD cups can immediately solve the sling issue - and with options, over an integral unit (a 9" for that barrel length) that has a mount built in.
For a future double stamp host upper, 10.3, 10.5, or 11.5 is money, and the short list of handguards would be the Mk18RIS-II, DD 9.0 (Lite or OmegaX), Centurion C4 9", LT 9.0 - any combination thereof would be just fine. The price point of the DD Mk18 complete and Centurion complete upper (if you prefer that rail) are hard to beat.
عندما تصبح الأسلحة محظورة, قد يملكون حظرون عندهم فقط
کله چی سلاح منع شوی دی، یوازي غلوونکۍ یی به درلود
"Being able to do the basics, on demand, takes practice. " - Sinister