The OS 15 cc gas engine would make a good combo. It is super runner and is very quiet on its muffler. It puts out decent power turning a14x8 APC at about 8800. That should do fine for a KS. I have mine on a tclip but had to stretch the tail to accommodate.

it tends to be a little on the heavy side so make sure you can balance the model with minimal or no extra weight added.

another possibility is a 10cc gas engine. I read that the Evolution 10 cc, current vintage, runs well and is quite a bit lighter.

Gas mileage of the OS is terrific. I have an 8oz tank in the tclip and it runs at least 20 minutes. I have yet to run the thing dry. I also use and highly recommend the Tech Aero IBEC to power the ignition.