Noah, yes Sir to both ?'s. Gas Block will need changing and this barrel has 1/2-28 threads.

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Noah, Features of CMMG, Inc 5.56x45mm Nato Mk4 Barrel Sub Assembly - 12.5inch Mr 4140cm Sbn, 5.56mm:
12.5"
Multi Role Profile
4140 Chrome Moly
Salt Bath Nitride Finish inside and out
1:7 Twist
5.56×45 NATO Chamber
Threaded 1/2-28
Carbine length gas port
.750" Gas Journal
Package Contents:
CMMG, Inc 5.56x45mm Nato Mk4 Barrel Sub Assembly - 12.5inch Mr 4140cm Sbn, 5.56mm

Hi Noah, Yes you need to change the gas block and Yes it is Threaded 1/2-28 ---Manufacturer Number: 55DDF0A
12.5" --
Multi Role Profile --
4140 Chrome Moly --
Salt Bath Nitride Finish inside and out --
1:7 Twist --
5.5645 NATO Chamber --
>>>>>>>Threaded 1/2-28 --
Carbine length gas port --
.750" Gas Journal