Not custom, but in case anyone was curious about what the insides of Isaac looks like. The only I reason I took him apart was because I broke the LED off (had to resolder that, haha) while trying to remove his helmet/head. Heh, I was attempting to improve the illumination in there.
Oh, and if you're looking for replacement batteries I suggest checking out the Dollar Store. Got a pack of 10 for a buck!
Unfortunately, I forgot to take a picture on the inside of the head before krazy-gluing it back together. I just ripped the front grill (?) of the head, then it was just a simple case of popping out the translucent visor (wasn't glued on). Afterward I painted the inside white, so the light would reflect better. Before doing so the interior was basically the same orangey-rust color as the outside of the helmet. You can kinda make out the white in the photos.
The waist is actually a ball and socket joint. If it wasn't for the armor across the stomach and spine, Isaac could bend forward and back.
And just for fun, what it would look like if you replaced the white LED for yellow, red, or green one. The one on the far right is the white LED.
Here's how it looks after I finished reassembling him together.