So I sense some disapproval of the diesel swap.
It's not our choice either, but I understand funds are a bit limited for what may be a $10-15,000 repair based on some prices presently on the North East Military site (and $23,000 for a C4 engine).
We have spare Detroit diesels here (although I need to confirm if any are 6V53's, Perry) and it sounds like a very interesting project to me. I really enjoy the design/fabrication stuff.
Anyway, I am working full time at a "real" job right now, but retiring in April so I will have more time then to follow up on the leads you all gave me above. In the meantime, we will continue dismantling to find out the full extent of the damage.