I haven't wrote a mortgage loan in over three years so things could have changed but IMO your best bet is to convince the owner to carry a contract.

Seeing as the property has multiple out buildings, a manufactured home, and another 70+ year old home on it, you are going to run into problems obtaining financing. Add to the fact that this will not be a primary residence and I would assume that even most community banks would require you to put 30-40% equity into the deal (Dogfish?), if they would do it at all. In addition it has river frontage, which is a potential flood hazard. Another ding against the deal.

I don't want to discourage you though. Any potential buyer, be it owner occupied or not, is going to have a tough time financing this property. Think about what that does for second. That narrows the pool of available buyers, which in turn affects the overall value of the property itself. Chances are that the owner of the property is already fully aware of this fact. This gives you negotiating power. If the owner really wants to sell the property he would be best served by selling the property with owner carried financing. You should be able to refinance out of that contract after occupying the property (and possibly improving it by removing the MH) for two years and at that time pay the owner in full for the price of the original contract.

There are plenty of people out there (and here) who could help you and the owner come up with a mutually benficial owner carry contract.

Best of luck to you.