Head - Dynamite (Sgt. Savage)
Arms - Salvo
Torso - custom cast (Billy from Predator)
Waist - Footloose
Legs - Roadblock v4
Rifle, rocket launcher - Marauder Inc.
Satchel - Elite Force (I think)
Gyrene is an original character. He started with the head, which is from the Sgt. Savage figure Dynamite. Even though the Sgt. Savage figures are a somewhat larger scale than the correct 3 3/4" scale. However, the heads of ARAH Joes tend to be somewhat on the large size in terms of scale, so the Sgt. Savage heads actually fit in with ARAH figures quite well. I also used Dynamite's filecard to decide on a specialty, but rather than just straight-up demolitions I decided on a Marine assault man, who is trained to assault fortified positions using rockets, explosives and breaching techniques.
The first couple of Marines among the ranks of the Joes had a specialty of 'Marine'. So I consider Gung-Ho to be Force Recon based on his filecard, and Leatherneck to be a Rifleman. Other Marines in my Joeverse (some based on explicit details on their filecards, some from inferences) are Sgt. Slaughter, Mainframe, Bullhorn, Blast-Off and Mirage (since they're Mega Marines), Cross Hair, Hollow Point and Ice Storm. None of these are assaultmen, so that was a available. I tend to do a lot of thinking about where an original character fits into the unit. I've also done four customs, so far, of Marines: Cool Breeze, Jarhead, Tracer and now Gyrene.
I needed a fairly bulky torso for Gyrene, so I used a custom case I had on had, which is for Billy from Predator. I'm using the Billy head for another custom, so his torso was available for use. The arms are Salvo, waist is Footloose, and the legs are Roadblock v4, since again I wanted something big.