Moving a wall isn't that difficult nor expensive.  

If you're not completely opening up walls then it could be less.Regarding financing, I don't think the option of closing on it and immediately getting an equity line will work, because they're going to use the lower of purchase price or appraisal.  

Nail the guy to the wall!

On top of that the units themselves get very little wear and tear because guests are using things like the kitchen to cook or putting holes in the walls to hang personal pictures. 

All that said I love older homes and have owned a few  however accidently digging up your septic or opening a wall to find it used to be a shed teaches you to be cautious.

Sometimes its best if you just buy an empty lot but other times it may prove advantageous to do a remodel leaving the foundation and one wall up.

What I was saying is that I have hit many walls, and I haven't given up.

v=IPM8OR6W6WE- problem valley in a roof, that keeps accumulating leaves and easily leaks- Commercial property that attracts graffiti artists - paint won't stick- Walls in bathrooms that don't have great ventilationWhat else can you think of.....?

What is the rehab cost difference in leaving it as a duplex vs tearing down the walls and reconstructing it?

The electrical runs are fished through walls.