Stuff happens, so you should always be prepared with an alternative option. 

Options or Alternatives?

Alternatively, just take title to the FL property with a FL LLC.

I would rather buy a $600,000 house for $25,000 down (3.5%) and buy another investment property for $400,000 (20% down -> $80,000), than buy the same $600,000 house with 20% down ($120,000).Alternatively, by opting for a 3.5% down FHA loan you could take the $95,000 difference between 3.5% down and 20% down, and invest that money in the stock market.

If you can't get traditional financing for whatever reason, it's not a bad alternative if it's a great property that will handily cover your costs.

Its not what was intended for the FHA program, but alternative uses for stuff always come around..Also, what have the lenders told you about other loan products? 

I have a variable annuity that represents 1/3 of my retirement assets. The other 1/3 is in a rollover IRA which I’m gradually converting to a Roth. I am 64 and would like to explore the best options (if any) of invest...

Especially considering what alternatives you have (or don’t have) for that money if you sell.

Gotta be patient now or find alternate means!

One alternative is to utilize leverage up front and set the balance aside in an account as @JD Martin mentioned, and re-evaluate your position every six-12 months.