Hi Steve
Look at the Wildhare RC website in the download page, you will find out very good technical information for the first gas engine users.
http://www.wildharerc.com/Downloads/intro.html

Any of these 50CC DA, ZDZ, 3W, BME or Brison are powerful, light and perfect for 15-18lbs and aerobatic 3D planes give unlimited vertical. Use google to find the websites and you can compare prices to order the one that you need. A 50CC would cost around 495 to 550$US.

Which plan are you using to build the Edge 540? I am very interrested to sratch built one in the 28% or 29% range and 80 to 84 inches span. The only one Edge plan that i have found is from DL Design...
Daniel