Cool truck!
From what you described, it sounds like the throw out bearing to me. The next time you hear the noise, lay your foot on the clutch pedal, don't press it all the way down, just lay your foot on it. If the noise stops, then it's probably the throw out bearing. If the noise continues then you may have a more serious tranny problem. Have you checked the fluid in the tranny/transfer case?
I hope it's a cheap and easy fix, man
Post more pics of the truck!