Nowadays, it will be difficult to break Maynard's RC plane record. Our modern RC systems do not have the range like that old RC system he used. Plus you would need a special permit in the USA to attempt it too. The FAA has to approve the flight and record attempt. You would likely have to make the attempt from another country that doesn't have stringent rules against such flights by RC planes.

Maynard used a huge set of binoculars on a special moveable chair setup to allow him to see the airplane that high up. I suspect that chair and binoculars was something that was surplus from the military for high altitude observation from WWII or thereabouts. Maynard also got permission from the Navy to let him use their Naval base with restricted airspace to attempt the record flight too. At the time there was the cold war and the military and government weren't about to let the Russians beat them at anything.

Yeah I believe he did use a Fox .59 RC engine in the plane too. He did some pretty good adjusting of that needle valve on the engine to have it still work at over 13,000 feet up from almost down at sea level too. I beleive that his duration record was set using a Merco .49 engine.

I am surprised that the Russians didn't try to best his record later. At the time both of the countries were pretty competitive in all kinds of things.