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The "quad-50 half-track" would have been an M16 anti-aircraft half-track. As such, he will presumably have served with an anti-aircraft unit; these seem to have been the only units employing these.
All of the eight US divisions had an automatic-weapons AAA battalion attached (originally just a single company in some cases, but later scaled up). A number of other battalions were sent to Korea in support roles - in total, there were eight divisional battalions and six independent ones. However, per that source, only the divisional battalion seem to have used the M16; the independent battalions may have used towed quad-mounts instead.
I have not been able to confirm the table of organisation for a Korean War battalion, but I believe it was the same as the organisation used late in World War II. If so, there is an overview of the battalion structure here (39 officers + 796 men, 16x multiple-mount .50" and 16x 40mm), plus a breakdown for the headquarters battery and the four gun batteries, although the second document seems a little confusingly laid out. A battery would have had six officers and 172 men.
The doctrinal manual setting out how these units should be used was FM 44-2 - again, unless this had been replaced by 1950. As you note, in Korea they were frequently used for ground support; chapter 8 (p. 93) sets out how this was expected to work.