Yeah, I've never seen this before on other vehicles or in the TM. I'm not sure what the bolt goes to but I need to get the rig going. The fuel tank was empty so I put some fuel in it and it didn't leak around the bolt so guess I'll figure it out later. I'll re-post when/if I pull the tank.
On another note, I finally got the rig running last night. New glow plugs and fuel was all it needed! But, there is no oil pressure so now I have more important issues to figure out. After running for 15 seconds, the oil pressure light didn't extinguish. Pulled the new oil filter and it was mostly dry so I think the oil pump is bad or the intermediate shaft is bad. Or, maybe the oil pump somehow lost it's prime? The truck has been sitting for at least 1-2 years.