Now, there is nothing like 'general US WW2 pacific' or you have army or you have marines. Equipment is indeed different. Gothic Line US troops are not suitable to be Marines and in 28mm not for US Army in tropical uniform.
US army tropical uniform was a standard HBT (like the USMC one) but with Army webbing and boots. Army did not usually wear camouflage covers on their helmets or camo netting.(A good reference is the illustrated history of US Army operations on the PTO available as PDF from the Center of Military History.
In 20mm a good approach is to take late marines without camo covers on the helmets.