We currently have a car lined up with Thrifty and they have a shuttle service to and from their Cape Canaveral office.
It is a 50 mile drive from the port to MCO and it can take an hour to complete the drive. In 2004 my cab driver broke a few speed limits and knew the way like the back of his hand - as I recall we made the run in around 40 minutes. Oh, there are tolls too and we had a speed pass for those.
I know I am sounding bleak, and if the stars all align with the moon you'll make your flight. But doing it with a rental car might be taking away any slop you have in the timing. I suggest contacting Thrifty and see what their policy is about helping to expedite people with early flights. I imagine they encounter this scenario often and they might have a plan to get you on the road fast.