i sailed in the engine room of that ship in the early 1970s and know that most of the smaller usuable parts of that ship were removed before circle line got rid of her after 1976 the main engine was partially strippedIf it were me, I'd start with verifying the crankshaft is good and take any opportunity to get a spare crankshaft if any ever surface. There was another old boat with a different model Fairbanks Morse, the John Cobb, that broke its crankshaft back in 2008. That's the kiss of death for any antique engine in my opinion.
I'm not an expert, but I think I know some stuff. Here are my thoughts. A strain gauge can show bad main bearing alignment. I'd first use a strain gauge. If that shows the crankshaft is flexing any at all, get the crank magnafluxed or just run away. I think it can be magnafluxed with the crank in the engine. If the strain gauge shows zero, make sure the crank has contact with all the bottom mains. If it is in good alignment, not flexing, and it has contact with all main bearings, it's probably good to go as long as you keep it that way. Good luck. It's always nice to hear of somebody trying to save old iron.