ok you first picture looks the bestr place to mount it drill 4 holes on a metal plate and buy about 5mm longer bolts this wont hurt the motor at all also if u want u should weld
a bicycle axle just above your rear tyre then bolt that plate i told you about to it dont worry its even weight on the typre and on the mount hope this helps heres basically
how i built it except with this guys mount obviously yous is guna be custom like i surjested heres da link
YouTube - how to make a homemade motorized bicycle hope this helps ;D
YouTube - how to make a homemade motorized bicycle
thats your anwser but hang on the mount is crap you can use mine if u want first buy a metal plate then drill 2 holes according to where the screws are attached in the muffler.
depending on how thick the plate is you may need longer screws and yep thats pretty much it.. i was wondering if you had any spare working motors please? message back if you do
good luck david.