No serious civilian drone operator would use anything less than a Hirth S1218 as a reliable engine. Dave, seriously, can you imagine the banging and thrashing noises of a four-stroke when stealth is an absolute requirement? The noise from the tappets alone would give warning from miles away! Now then, I admire your efforts and for that, should you send me your address (not the one in the Caymans), I will send you some parts from an old Puch 'twingle' which you can use as a paperweight or as a conversation piece at your next Bar meeting.
I've still got an XL500S I am putting together. I will never run out of 4 stroke singles. However, I also got this. It should make Bro Chuck happy.