No. The Yankee Hill Machine R9 will be compatible with the YHM 3-Lug Mount and YHM Nielsen Booster Assembly. The Yankee Hill 2045 3-Lug Adapter Assembly can be found linked below:
https://www.opticsplanet.com/yankee-hill-2045-3-lug-adapter-assembly-1-3-8-24-tpi-aluminum-stainless-steel.html
The manufacturer does not state the OD of the Yankee Hill Machine Phantom 5.56 Q.D. Muzzle Brake 1/2x28. I recommend contacting the manufacturer for that information.
Yes, the Yankee Hill Machine Phantom 5.56 Q.D. Muzzle Brake is compatible with all Yankee Hill Suppressors designed for 5.56. It will not fit .30 cal suppressors.
The Yankee Hill Machine Phantom 5.56 Q.D. Muzzle Brake 1/2x28 TPI YHM-5M2-QD is 2.5" long so the shortest length barrel would be 13.5".
Yes, it is compatible with YHM Resonator R2 .30 cal.
No, this will not be compatible.
It will work.
Yes this will work.
Yes this will work.
According to Yankee Hill this muzzle break comes out too 2.5in, which should bring your barrel length too 16.2in if pinned and welded.