The 16" Wheels are fine just change the tires to P225/55R x 16" XL (extra load). You will be amazed at the difference this tire makes to the van. Over the years the 3.3 drivetrain kept getting bigger tires but they never changed the final drive ratio to compensate. Even the van alone will be much more driveable and it will handle much better as well. You might want to put on a light weight distribution such as a 600 pound Eaz-Lift.
It sounds like a great Rally, it is a rough time of year for me to break loose but you never know.
looks very nice!