Looks like a tight fit. What are your plans for mounting it? I used the Cranbrook for my 49cc four stroke build, seems like a solid frame. Check all the bearings, the factory puts almost no grease in them. People complain about the coaster brake, mine seems good so far, although I use it sparingly. I put suspension forks with disk brake on the front and added a caliper brake on the back.
I am planning on using industrial tubing clamps and a plate at the back of the motor, and plate coming off the pto surface connecting to an L bracket, and a third tubing clamp in front. A little tight, looks like it was made for it.
Some progress. I have the motor temporarily mounted in the frame. I screwed up the offset, so I will need to fix that, and If still needs a front mount. The concept looks good, motor fits just right! Most of the machine work for the gear reduction is done. Just need to press in bearings. My 3D clutch is here, and I have a plan for a 5/8 to 3/4 shaft adapter. As you can see, the gas tank is mocked up. I will use the posterboard as patterns to cut out sheet metal, and weld or braze it up. Planning on two tanks, one on either side of the top tube.