From what you say is that they are not legal to be there based on today's zoning (non-conforming), but they are legal based on when they were installed (legal).

I have installed a mailbox and address numbers.

That's not a 'bad' rate to borrower very accessible capital that has to be repaid over a generous 360 installments. - Most DSCR loans come with standard 3-5 year early payoff penalties.

They look like they are mostly metal.

This is what I got from the seller.Remodeling: No remodeling has been done recently but is still in good condition and almost like new: a new 50-year metal roof; new central air and heat; new cabinets, sinks, etc., in the kitchen and baths; new flooring; a new driveway.  

Granted I have my own guys to install.

If it were mine, I would have the same company come out that did the install and refurbish the area back to its original condition.

Shazam me taller Uncle Sam.....

I'm looking to install a new furnace in my duplex in Cincinnati OH. 

Depending on the facts and circumstances of the agreement, it could either be treated either1) the sale occurs as of the original agreement date, and then your taxable gain is generally spread out over the life of the principal payments as an installment sale (although I should mention any depreciation you've taken on your property could affect this), or2) the sale does not occur until the lease option is exercised, and gain reported at that time.