peugeot Ludix with speedfighter 100cc engine

Will a 100cc engine out of a metal x same engine as a speedfighter 2 fit in to a 50cc ludix they are both air cooled engines just want some advise before I take the time to rip both engines out and have to put them all back together as I only have 1 day to do this before I have to go back to work

 

Don't worry just realised the engine is lay flat instead of up as in the speedfighter

What 100cc ore 125cc engine will fit in the ludix

Ore will I be better off getting a 70cc kit and some sports parts