I've developed a habit of replicating any 6" scale custom I really like into a smaller, GI JOE 3.75" scale format:

::Parts this figure's made from:
-GI Joe Snake Eyes (torso, pelvis, legs, hands)
-Hasbro Indiana Jones Mutt Williams (jacket, arms, lower legs/boots)
-1990s GI JOE Swat/tactical figure (head, neck removed, resculpted with a dremmel, hair sculpted with Aves)
-GI JOE Venom & Valor Marine/Mech figure (Sunglasses)
-Star Wars EP 1 or 2 Clone Trooper (Chain gun, dremmel modified to resemble a modern chaingun, repainted, magnet added inside ammo chamber)
-Ammo belt for chaingun was once part of a ML Longshot belt accessory, cut down, painted, and a magnet affixed to one end. Ammo belt clips into the chaingun, and is removable.
-Shotgun was a black plastic casting, purchased online (shard of Neonium magnet glued inside)

::Design Process
-Installed a disc-shaped Neonium Rare Earth magnet inside Arnold's back, before painting and his jacket were put on.
-Carefully dremmeled down the inside of Mutt William's jacket to fit Arnold's Snake Eyes body.
-Superglued glasses to the repainted/resculpted head. Affixed the head to the body using the Aves Sculpt-trick.
-Painted eyebrows, and the hair dark brown, drybrushed hair with a lighter brown
-Painted undershirt black, and drybrushed Blue-Gray Vallejo Acrylic paint
-Dremmeled off Snake eyes holster and leg-gear, sculpted over using Aves
-Spliced Snakeeyes lower leg (below joint) into Mutt William's pant legs/boots. Used paperclips and superglue like rebar to reinforce this, instead of just gluing the two parts together. Sculpted over using Aves.
-Painted the shotgun, and sealed all accessories and the primary figure.
-Put the jacket on Arnold, painted the arms/jacket to match using Vallejo Black acrylic.
-Sealed the entire figure with Vallajo matte finish varnish.

Later on, I picked up a Mutt William's / Motorcycle pack for $3.00 at Walmart.
-Cut off the existing saddlebags, and added squarish side-packs (similar to those in the T2 movie-bike), taken from a ML Mad Jack utility belt.
-The background that Arnold/Bike are displayed on came from a random a website auction - I haven't a clue what set it's from - but it does look good. :)

I'm really happy with how this figure turned out, complete with it's magnetic attachments. ^_^
Also visible in the 3rd photo is the 3.75 custom built T2 Endoskeleton figure I made a few months before this one.
Check it out here at Figure Realm under my user-id if you're interested. It was built months before any T4 mini-figures were available using a 1990s Endo minifigure and SW Droid parts. :)