opinions... project:not so smart

Might be easier, but have the same effect, to do it to a Honda Insight (the first generation, not the new ones they came out with). It's as light or lighter than a Smart car, and a little longer, so you might need to lengthen it as much, if at all. Also, they have a fairly large rear hatchback area that you might even be able to make it a rear-engine car, but then you would have to stretch it for sure.

I saw a video of a couple Smart cars with Hyabusa engines, and they were screamers.