You cant put what ever you like, It just take time money and effort... Aswell as after a point... it wont be a Manco....
GY6 doesnt have the same or near same footprint as the tec/BS/clone motors they have had...
Offhand Itll need a bunch of work... Probably modifying the whole rearend to accommodate the length.
For the most part.. itll be better to just go with a big block clone....
Yeah, this guy on a buggy site was talking about how the torque converter system was so much better than the comet, but after looking at about 10” on the distance on the shortcase, I figured it was probably just tor the chinese karts.