RE: Viper Help
Did you order a full pipe or the Jett-Stream muffler from Dub?
The 600/700 flat packs would be prefered. Install them just above the aft wing hold-down bolt blocks up against the bulkhead. Make sure the resulting installation does on interfere with or get hung up on the aileron torque rods and pushrods when the wing is installed.
Your CG should be just about right when you install the exhaust system. Balance the plane at 2.750" - 2.875" for the first flight (dry). Aft of that back to around 3" is ok....... not suggested for the first few flights.