Slim profit with this scenario, but do-able.My question is regarding the bank accepting an offer for less that the payoff amount.  

(Taxpayer Relief Act of 1997created IRC Section 121)Thus the likelihood of making the cut is slim.

These rarley come on the market with both sides or both units however, so its slim pickings out there right now.  

Businesses with high volume and slim margins can go to losing money real fast in the marketplace.The businesses with good sales and fatter profit margins can sustain changes better.

I've done some of Rent-to-Own in the past and I can tell you that the likelihood of a tenant actually being able to get lending in 3 years is pretty slim.  

But, the pickings have become really slim.  

Margins are slim on this deal as the ARV is 60k. 

You mentioned FHA financing, this is a great program only requiring 3.5% down payment however this would require that you live in the property for one year, also since it's such a competitive market the chances of an offer with 3.5% down payment being accepted is slim (unless you find something off market) since other investors are putting down well over 20% which is much more attractive to a Seller.

When this happens, your prospects for profitable exit are slim.

Numbers do seem a little slim for me but I'm not sure what your exit strategy is.