A european thumper somewhere between 450-650 cc. A euro thumper somewhere around 450-650 cc, depending on your idea of nimble. I'd probably pass on that, it's expensive and takes a lot of time, blood, sweat and tears to create a monster...for what, a heavy bike that might not work as well as you imagined? Really though, there's many good single cylinder adv platforms available that just need a simple fairing and minor modifications to be more comfortable on the long rides. I like Noah's bike for instance. You could put one together in a few weekends and be done with it.