Hello cc Welcome to the forum glad you joined us
I have never bought off E-Bay, I've heard good things and bad things.
I'm not sure what bike you plan on using but if get lucky you may not have a problem mounting the motor.
I drilled my frame but I will NOT recommend anybody do that.
I had a bunch of links for solving that problem so you would not have to drill the frame. But I had PC problems and lost all my links.
Here is some links.......http://motorbicycling.com/f6/oversiz...olved-171.html
I believe boy go fast has a mount for sell that will solve that problem...it should be in one of those links