I don't see the point of recommending Jett mufflers. They are great, don't get me wrong, but for $90 a pop they would be a considerable investment for the program. They make a lot of sense when you have a .46 and you need just that little bit more oomph, or if you are racing and the class you are in won't let you go any bigger on the engine displacement. The kind of program this is could use any engine currently produced; the teams would simply have to build planes that performed with them. Take the baffles out of the stock OS muffler and let the teams pick whatever props they want. The planes will be plenty fast and the engines will last a good long time provided the teams learn how to tune right.
BTW, tuning right is more than just peaking the engine on the ground and going a touch leaner. A properly tuned engine is peaked in flight in the leanest scenario. With the kind of unloading you guys are going to be doing, that could mean upwards of 1000 rpm rich on the ground. Unless you want to buy lots of replacement pistons and liners, I'd invest in some telemetry so the teams can walk their way up to that peak setting without getting overzealous in leaning out the HSN.