Hey cain, welcome to the forum. If You do decide to build, I am sure you won't be disapointed. these are really fun to build, work on, and OFC ride. This is the website that I found to be interesting when trying to find out the history like you About Us
As for a frame. Just find one that you really like, make sure that there is enough room where the motor mounts, and then figure out a way to mount it. There are various different ways to mount a motor if the tube is too big. You can buy motor mounts, and sprocket adapters, which help making mounting alot easier, and safer. Good luck on your build if you decide to, and don't let the bug bite you if you do build. I just started 2 1/2 months ago, and I am on my fourth build already.