Trust me, you find your cadence, and I bet there will be others right there with you!! The trick to RAGBRAI, is make it your own ride...find a cadence you can live with, spin 'er up, and enjoy yourself! That's the way I do it.
While I am an International Harvester fan, your JD paint scheme tandem will fit right in! There are many who do indeed don costumes...Lipstick Man, Cheese Heads, and all maner of superheros. I am content to wrap my portly self in spandex...seems to be costume enough!!