The service coat worn in the above mentioned link does look like the 1911 cotton service coat.
As far as the basic equipment worn by an early U.S. Army automatic riflemen:
The gunner would likely not carry a rifle, so he would probably wear a pistol belt, pistol magazine pouch and a holstered sidearm instead with a canteen, first aid pouch and perhaps a bolo knife attached. If the automatic rifle was part of an infantry company the gunner would also be in possession of a 1910 Haversack and the equipment associated with it ... if he happened to be part of a cavalry troop, the gunner might be wear a pair of 1907 Equipment Suspenders instead of the infantrymen's haversack.
Assistant gunners, were likely armed with rifles. Therefore a rifle cartridge belt would be worn along with the above mentioned field gear. If not carried by the gunner, then the assistant gunner might wear a bolo knife instead.
Rifle cartridge, pistol belts and canteen carriers would all feature either rimmed or rimless eagle snaps and could be any of the 1903 through to 1910 patterns.
Holsters could be for the 1909 Colt Revolver or the early 1912 "swivel" style for the 1911 Automatic Pistol. The pistol magazine pouch would have featured either rimless or rimmed eagle snaps.
First aid pouches would likely be either the 1907 or 1910 pattern.
Bolo knives would be either the model of 1909 or 1910.
Additional equipment that might be issued to an NCO in charge of the gun or the squad might include a map/dispatch case (Model of 1910) or a pair of field glasses.