An STC IS NOT REQUIRED to add 3-point diagonal shoulder harnesses to the front seat positions of a Cardinal 177 or 177A that did not come equipped with factory installed attachment points.
This can be accomplished by the incorporation of one of our "Minor Change Kits". There is no welding, drilling, riveting, etc, - nothing that would require an STC.
Restraint assemblies and the Minor Change Kit are sold separately. Minor Change Kits can be added from the restraint page.
FAA Brochure on Seat Belt Safety Minor Change Statement (also available on harness pages)