Which documents can sometimes authorize deviations from an aircraft's original type design?

The correct answer encompasses key documents that are pivotal in authorizing deviations from an aircraft's original type design. GACA Form 8320-1 and FAA Form 337 are specifically related to alterations or repairs made to aircraft, allowing operators to document changes that deviate from the original specifications.

Supplemental Type Certificates (STCs) are crucial as they are issued when a modification has been validated, ensuring that the change meets safety and regulatory requirements, thus granting legal approval to the deviation. Airworthiness Directives (ADs) represent mandated actions to rectify unsafe conditions found in aircraft, which could also necessitate modifications that differ from the original design.

Together, these documents support the certification process by ensuring that any deviation maintains the aircraft's airworthiness and complies with regulatory standards. The other choices consist of documents that may provide guidance or information but do not carry the regulatory weight needed to authorize deviations from the original type design definitively.