I found this out after I sent you the PM. I believe Billy is wearing a "ERDL Boonie Tropical Hat". This was issue in Vietnam. I believe this is the hat since he is wearing all Vietnam Era issue gear. Except for a few items. His boots, are the pattern 2 Jungle Boot (Black Leather/Olive Drab Green Canvas). His Fragmentation Vest (Flak Vest). Right side of his Webbing Belt was a Universal Ammo Pouch (M1956). With one M67 Baseball Grenade on the left strap of the ammo pouch. Two plastic canteens on his back with canvas canteen covers. On the left side of his belt is a Compass/First Aid Pouch. Web belt topped with the suspenders. Everything he is wearing is Vietnam Era issue except for his IMI .44 Magnum Desert Eagle in his Cordura Holster which leads me to believe it's a holster from one set, and then a suspender from another set. Then his Machete which is on his pant belt not his webbing on his left leg side. Then he is carrying the larger Jack Crain Knife out of the two tapped upside down on his left side webbing gear suspender. Then he is wearing a medicine man pouch/necklace.
I hope you don't mind me bringing back this thread, and giving such a long winded message. I really hope this helps you.
-Andrew