I understand to do so, I will need to convert it into a self-directed IRA.

His response was that I would need to convert his work to HTML/CSS first.

It sounds to me as if your partner took money from you as an investment in a fake company and converted the funds for his personal use.You need to take legal action before he gets a mortgage on the property or finds a buyer.You have already said he is less than honest.You also mentioned a quit claim deed.  

They also gave me the number to another vacant structure that could potentially be converted.

Also, some of the small multi-family built in 70s and 80s in Iowa have wood foundations and most properties above a duplex are zoned commercial (much higher taxes) so you have to form a Coop or Condo (S Corp) to convert to residential status to drop the taxes.  

the downstairs living room was converted into a third room.  

THE best lesson  JUMP in and do it  DO IT   DO IT  yes jump in  me high school drop outbut have made lots of money more money than most people dream about  also lost a lot during the recession but always keep positive attitude  just signed agreements  to purchase  two more buildings to convert to self storage which will make it 5JUMP in 

Using Options and Corporate Pension Plans to Convert Equity to Income with Minimum Taxes.

I know here in Chicago people sometimes convert basements to units by adding a kitchen an bath.

Another opportunity I have, because of how the property is laid out, is to convert a storage room into a studio or 1 bedroom unit.