The 140cc lump actually fits into this 1960s C105 frame, with only a very minor amount of trimming, mostly around the upper mounting bolt area of the frame.
I have the carb mounting forward in this picture, but it also fits pointing rearwards. It barely clears the main downtube.
Carb pointing rearward:
I also had a couple extra front sprockets I bought for the C110, so I swapped it out for a 17-tooth 420 sprocket. I'm hoping this will give fairly long gearing, so it won't be buzzing at 40mph.