While this forum has many OEM motorcycle owners, there are a few of us around that have built them. You can ask questions here, but I do agree that elmoto.net may provide a more fruitful response.
On my motorcycle (since sold), I used a K91 Advanced DC motor, then moved to an AC20 motor. They're great motors, both of them. It all boils down to budget. Pick one. Don't say there is none, because that may mean you've got $15k to spend, which would make a nice bike. If you say $2k, its much harder to build something.
What kind of acceleration? range? top speed? (I realize you said 20 mi and 70mph, but that was a goal, not max figures).