The basement could be full of water, foundation issues, or there's mold on every wall.  

The issue I'm seeing is a note about foundation repair on a property has flooded.

It all depends... if the mobile homes are on permanent foundation.If they are not currently on permanent foundation, but can convert to such, then they become real property, and can get appraised as such.And, then of course, be prepared to pay more in property taxes as well.Instead of paying property taxes only on the land, appraisal will be much more including the homes, once they become real property.

We do see a bit more maintenance in those MF duplexes at they tend to be turn of the century homes with turn of the century issues - shifting foundations, galvanized plumbing, pop fuse electrical, ect. 

Our second flip - 30 ft of the foundation had collapsed in and the house was caving in on itself.

Some challenges we have faced are bringing electrical up to code (if you change so much as an outlet or light fixture, it's a requirement in my state) and house settling that makes all flooring except for carpet a challenge (contractors will want to put in all new sub-floor or they can't promise their work will not be without many issues).Hopefully, your foundation is good. 

Regardless, once you find a solid foundation, it may create a more flexible situation for you to make your "next move".

His grandson gives the historical account that it has railroad rails in the foundation. 

It will provide you with a good foundation of the process.When you are ready find a good General Contractor (or 3) to walk a property and give you a bid.  

This is my first post in the forum as I recently became a BP member :)My husband and I just got a Duplex under contract that requires significant repairs (no structural/foundation work) as it is quite old and has extensive wear and tear.