RE: Engine choice for GP Learjet
The jett-stream muffler is a tuned exhaust. Much like a tuned pipe. Bolt it on, get an instant extra 1000 rpm or so (or more like 1500 depending on the prop) above the stock muffler. No muss, no fuss. Available direct from jettengineering.com
On the OS.50/jett-stream combo on the lear, run a 10x6 prop to start with. Should be able to move up to a 10x7 after initial flights, and still keep the rpm up.