This is precisely what's done with all CL stunt engines plus they keep the weight as low as possible (I have a rear exhaust ABC .61 that weighs 12 ounces with muffler). The cheapest would be the CL version of the Super Tigre G51 (an exceptional engine BTW) and ranging up to things like the RO-Jett or PA (made by Nelson).

The problem with RC is that the market is driven by a fascination for high HP numbers. Take the Super Tigre G51 for example. The RC version develops around 1.6HP@ 16K but the CL version is 1.1HP@ 12K (or thereabouts, I'm going from memory here). Which one will the average RC flyer choose even though they usually prop for around 12K anyway? I know which one will swing a big prop the fastest.