Would the FAA or whoever certifies the airworthyness of a restoration allow that original fuselage to be used, or do you need to build a new one using the original as a pattern? Bob
Depends upon condition. Major repairs would have to be documented by a form 337, signed by an Airframe & Powerplant mechanic with an Inspection Authorization, to certify that "approved" methods were used for the repair. The 337 is sent to the FAA who reviews it and ultimately approves it. Typically for a metal airframe, it would need to be sandblasted, inspected for cracks and other structural issues, repaired as needed, inspected again, then primed & painted. This is fairly common and can be performed by someone with decent gas welding skills. The work doesn't have to be performed by a certified mechanic as long as he/she oversees the work (the mechanic has to sign it off and is the responsible party).
Rebuilding from scratch is OK but more problematic as it would be necessary to prove that you used the exact same processes and materials as the original, plus you'd need to fabricate a number of fixtures and jigs to maintain the correct geometry. It's been done but it's analogous to doing a high point restoration on an elite automobile, e.g. time consuming and expensive. This is mainly why you don't see a lot of those old birds flying. The temptation is to improve the design by using the better materials and techniques that are available today, but that can be really difficult to obtain approval later, as this falls outside the definition of "major repair" and becomes a "major alteration" which must have approval by a FAA engineer or designee, or must duplicate a previously approved alteration.
Wooden structures are handled in a similar manner except of course you are performing quality wood working (more akin to cabinet making than carpentry) and using some repair techniques and materials that are unique to wooden aircraft structures.
In any of the above cases, it's essential to involve the local FAA office early in the process to ensure that you don't go on a path that results in a very expensive lawn ornament.
This is why cars are so much easier to work on, and why you see a lot of old airframes hanging from the ceiling in upscale bars and restaurants.
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