New to this...Micargi Falcon GT or Micargi Rover GT

My first option is the Micargi Falcon GT (Black with Red Rims). Second option is the Micargi Rover GT. My concern is that the 66/80cc motor(Pirate Cycles) will not fit in the Micargi Falcon GT frame. It appears some have put a motor in them but not sure if they achieved it with the 66/80cc motor. Is there a big difference in the physical size of a 50cc vs. a 66cc. I really want the Falcon GT but not sure if it is possible and just want someone to confirm that they have seen it done with the 66cc.... Please help on my decision!!!

I decided on the Micargi Rover GT and play it safe for my first build! I really liked the red rims on the falcon but I can always add them to the Rover later. My Pirate Cycles Motor and bike are in the mail. I also picked up an old 1 gallon metal fuel tank off a mower that is in good shape. I'm planning to weld up an adjustable mount on the tank and hang it behind the seat post. I'm looking forward to start building it!!!