I can get a 30-year fixed loan for 6.630%.The property taxes 1,976 /year i.e. 165 per month. 

Also fully understand the refinance guidelines for any DSCR, or Traditional loan products you BRRRR into.

If its just deed than an attorney can redo deed and charge a recording fee but if a payment missed and mortgage company finds out they can request a total loan repayment.  

If you want less leverage simply put down the funds you would use to pay down the 6.4% rate on the new property so you are at say 60% loan to value on the new house.

I'm looking to use a Fannie Mae Renovation Loan. 

Most loans are sold to those two entities.  

Hi Kevin,I'm a licensed loan officer in the state of Florida, if you'd like to schedule a quick call, DM or email me!

Not a lot of distressed sellers underwater on loans.

Are you pre-approved for a construction loan? 

If so you could run the numbers on taking a loan on the zero-debt property to pay off the other.I'm still unclear on the goals - you've brought a lot of other things into the equation (e.g. paying of high interest debt, STR as personal vacation home, stocks/dividends, etc.).