Hey guys, just wanted to throw in my own $0.02 on the combination of a NuVinci hub and SBP shifter... I've had these two products together on a Micargi cruiser frame (looks kinda like the Cadillac frame you've got), and together they are amazing.
Well actually both parts are amazing just by themselves. But when put together, they are freakin' phenomenal.
At first, I had my bike rigged with the standard kit set-up (one-speed, left-hand drive), and the novelty was beginning to wear off and I was a little bored with the limitations of the bike. Then I plopped down the cash for the NuVinci and the shifter and it got really interesting again. Shifting gears (or ratios in the NuVinci's case) is a blast!! My top speed with a polished but otherwise stock engine is somewhere between 30-35mph, and I can accelerate from a stop without pedaling at all.
I posted a thread about the installation a while back:
Here is what my bike looks like now. Good luck with your Cadillac build, and let us see how it turns out when you're finished!!