I'm building an AS1 and I have the opportunity to use various parts from other previously airworthy airplanes. Mindful that the FAA takes a dim view of re-registering airplanes, does anyone know of any rules regarding recycled airplane parts in homebuilts? The fact that engines get re-used all the time tells me that there is some flexibility. But are there any limits to what can be recycled; an instrument, a wheel, fuselage parts? Any help I can get in running down the rules would be appreciated.