@Henry SimsThe more professional way would be to have Note and Mortgage document drafted by an attorney. 

If you are borrowing money, the lender would usually create a property mortgage document and record a lien on your property/land.

I currently own a single-family 3/2 in South Philly and the mortgage is about $1,900 a month.

As a mortgage expert, my advice would be to ensure the financing aligns well with your plans and goals.

That being said, it's going to be very near to impossible to find an investment property that will just cashflow (where the tenants will pay for your mortgage and then some).

If I were to rehab it, could I refinance with a conventional owner occupied mortgage at the ARV in order to pull out my original capital?

NOI represents the property's income after operating expenses but before debt service (mortgage payments) and income taxes.Evaluate Cash Flow: Deduct the mortgage payment (principal and interest) from the NOI to determine the property's net cash flow.

Your mortgage person can do it, too.

To find investment possibilities, consider elements including property pricing, demand for rentals, vacancy rates, and economic trends.Think About Financing choices: Investigate your choices for financing a possible real estate purchase, such as FHA loans, conventional mortgages, home equity lines of credit, or other innovative financing techniques.

I will definitely be using this for reference.https://realestatebees.com/mortgage-social-media-content/