I went to the Royal Garden in 1980. The Plaza did not exist then. It was a hotel with a couple of bars out front, one of which had a monkey swinging on a rope that used to grab at passing punters. The US navy used it as an administrative base when the fleet was in. Their MPs liaisoned with the Thai police in patrolling Pattaya and you could see them dragging the bad boys across the road and ultimately to the brig.
I do not think it was around during the war, but have no proof either way.