Here is a FAQ from the EAA regarding the 51% rule.
https://www.eaa.org/en/eaa/aviation...ent-rule-on-amateur-built-homebuilt-airplanes
Q: I want to hire someone to finish the wings on my kit. Can I do that?
A: There is no specific prohibition in hiring someone to help with the construction of your aircraft. In fact, that is what you are doing when you purchase a kit; you are hiring someone to help you construct your aircraft. To be eligible for an amateur-built certificate, the “major portion” (at least 51 percent) of the tasks needed to make the aircraft airworthy must be completed by amateurs “solely for their own education or recreation.” So you may hire someone to finish the wings on your kit if you still have 51 percent or more of the tasks remaining to be completed by amateurs solely for their own education or recreation.
To assist builders with assuring that they have accomplished the required number of tasks, the FAA has provided a
new checklist that enables builders to fill in an additional column for “commercial assistance” in addition to the kit provider column. This form helps a builder determine if the project would continue to comply with the amateur-built regulations if he or she hired someone to complete additional tasks originally evaluated by the FAA and kit manufacturer to be amateur-builder tasks.