Head - Galoob Unifighters
Arms - Beachhead
Torso - Crankcase
Waist, legs - Crankcase

Helmet - Sgt. Savage
Backpack - Airborne
Binoculars - Sneak Peek
Rifle - Marauder Inc.

The first customs I ever posted publicly were two versions of Duke. Some time ago I got a handful of Joe-like figures in a lot of fodder I bought, and was able to figure out that they are Unifighters from Galoob. Anyway one of the heads just screamed Duke at me: blond and square-jawed, and fortunately not smiling like a doofus as in the original figure. So I knew I had to make a Duke out of it. Actually, since I had two of that head, I decided to make two Dukes.

Unifighters are very slightly larger than your typical Joe, but Joes often have slightly large heads for their bodies so there's not really a problem there. But Unifighters do have a significantly larger ball joint for their necks than Joes do. So for this Duke, I trimmed down the ball joint to fit a Joe torso, and for the other I used a Unifighters Joe torso.