You mean the Genesis Two Nine, right? Seems there's an assumption you're referring to the Onyx, which IS difficult to build on, but doable. I'm 6'4", 280#, and LOVE the Two Nine. I was hesitant to build on an aluminum frame due to weight and the abuse I knew it'd get from it being motorized. My fears were allayed long ago; this cheapo Walmart bike is a quiet beast. It has held up to a great deal of unintentional punishment. I recommend you order an unassembled one and have it delivered though; build it yourself. The rear brakepads suck, so replace them. Make sure the rear spokes are tightened properly, and check the rear axle. The tires are OK, but you should expect to change 'em for better ones (700c's are great for asphalt). The Two Nine's down-tube is larger, so I recommend you get the larger front-mount. Like I said, I love it. I have had two potentially frame-bending/snapping mishaps on it, no exaggeration. That frame and the axles have stood the test of time, speed, and much more weight that it's rated for. Check out my pictures and a few of my older posts for details.
Oh, the rear is a 36-spoker, so the drive-spock fits fine.