Doug,
The short answer is... Maybe.
A few years back, the Feds got kinda nasty about "building an airplane from a data plate." The thinking was, "as long as you have a data plate, you have an airplane." That's still partially true, because if an airplane's data plate goes missing, you no longer have an airplane. (or at least you'll have a long, tedious process getting it replaced.)
What guys were doing was taking the data plate off of a TOTALED airframe, and then piecing together an airplane from spare parts and other wrecks. Absolutely NOTHING flying around attached to the data plate for AirKnocker serial number XXXXX had anything to do with the original AirKnocker serial number XXXXX.
This has led to questions about how badly damaged an airplane can be before it can no longer be rebuilt. Obviously, if the fuel truck backs into the wing of your 172, you can find a new 172 wing somewhere, have a mechanic put it on, have an IA dot ehpaperwork and go. Or, if you're recovering your super cub, and want to STC the big tailfeathers on to it, that's not a problem either. However, I know of a person who asked an FAA inspector while recovering the Cub, if it would be OK to:
1. Add big tail feathers.
2. Add the "wide" fuselage
3. Add Dakota-Cub metal wings.
4. Convert to 180 horsepower
...and go flying once the appropriate 337's were turned in. These are all STC's. The answer was NO, that would be building an airplane around a data plate. After further discussion, it was decided that as long as the local FAA office was kept informed of the ENTIRE project, FROM THE BEGINNING, before work ever started, and it could obviously be proven that these were all mods done during a re-cover, and NOT building around a data plate, it would be OK.
Usedta' a guy could slap a bunch o' parts from different airplanes together and call it a homebuilt. Not any more. If you do it as an experimental, you'll be able to get a NON-RENEWABLE TEMPORARY airworthiness certificate for it, but you'll also need to provide a reason WHY you did it. (Like research and development.) Not worth the expense.
If you are looking at rebuilding a wreck, get with your FSDO first to make sure they buy it.