Is there a way to get a construction loan with the original property still on the land so I can do a new build on part of the property and then slowly rehab the historic property?

Easy Street Capital is a great hard money lender and they have an easy to navigate and quick draw process and CV3 Financial was able to assist with the refinance.

My understanding is very unlikely unless the deal is beyond stellar and you can provide strong financials and experience. 

Not really necessary.You will need a commercial loan refi with higher interest and maybe more down to cover it.

I know there are some DSCR type of construction loans that don't factor in DTI.

Get the cost analysis and blue prints done and work it out with the construction loan committee and start the work draw phase.The other options which can be a little easier is buy a home that will pass an Inspection/appraisal and not be "Subject to" but does need a lot of TLC/renovations and do it yourself.

If the buyer got a loan from a traditional lender to get to the 75k number, would that automatically put me in a second position on my seller financed note?

@Jake Posner- thanks for the post ...if you plan on needing financing for the rental proeprty - make sure to get  fully pre approved  for the hypotehtical  scenario you are planning ...use a loan officer or lender that is licensed is all the states  you are looking at . thanks 

Do you know if the loan is backed by either Fannie Mae or Freddie Mac?

We will finance the 25% down with a loan at 3% from a life insurance policy loan and hope for the best on the conventional investor loan we will have for the purchase money.