I have an old one of these, I was going to put a 15cc petrol two stroke in it, I thought the 10cc may not quite be enough.
I the end, I just couldn't find a way to get a newer engine to fit as well as ignition, battery etc on the rails.
She got an old Magnum 91 FS today, and only needed a small amount of hacking to fit the rear mounted carby in.
Good luck with it, they are beautiful old kits!
spud