What year is it? Early ones ran hot and were known for cracking pistons. If this one has never had the engine gone into, I'd wager it's a later one that is putting out closer to rated HP. If it's an early one with Ford decals, look for excessive blowby.
Yes, front duals would worry me. That axle (Dana 70) was never intended for duals, so I would take a look at the final drives VERY close, along with the front diff. Ditto pretty much everything else Rod said.
Having said all that, they were one bad a$$ machine for their time.