RE: NitroPlanes - MQ-9 REAPER
I guess in theory you could (nitro engine), but it would take a lot of mods if you did not want the engine sticking out of the fuse. You could mount the engine forward a bit so the head is in the air intake area and use a balanced and bearing supported shaft to drive the prop, but you would have to make mods to the rudder and elevator controls and the fuse formers in the rear. And then also making a place or space for the fuel tank, whichwould probably have to be remote requiring the use of a pump and then you would probably end up wih CG issues.
I'm not sayinng it can't be done, but it would take a far amount of work, and not for the faint of heart. If you do decide to do it, Ithink a lot of people would be interested in seeing it.
Good luck.