The engines you have will get you in the 120 mph range with the right prop. Considering that plane comes with an adjustable back plate mount, you can use one of your existing engines, and if you want more speed you can switch later.

I have no idea if you plan to race this plane, but if it is solely for Sport use I would recommend the Sport Jett .46. If you check the Hangar Sale at www.jettengineering.com Dub typically has them on sale at $220. Still a bit more than your average sport engine, or the Rossi, but it is a very nice engine that you would be extremely happy with. The Jett should get you close to 160 mph on the Viper.