Coming downhill on narrow, curvy, mountain roads at 50+ mph can be scary. Especially when there's a 50+ foot stone wall on one side and a 50+ foot drop-off on the other side.
I can understand you wanting to build a go-fast bike. Hell, we built stuff like a 6' long motorized skateboard you sat on.
A project like this is going to require paying attention to every minute detail. Right down to every little ball bearing.
If you're up to it, give it a try. It can't hurt you after it kills you.