I would check with the zoning first. If you are lucky, it might be R2 (meaning it can be a duplex).
I once had a R2 building, and it was a legal 4 plex...
fire-rated drywall, steel doors, fire escapes, and electrical separations will be very costly, if in fact you can convert.
Simple answer is to check with your city and take it from there.
Kir.