Here is a link to the Sonex website with their checklists, as well as the "letter of elegibility" showing that the FAA has already approved these particular kits per the 51% rule. Basically, if YOU built the plane from one of these kits, you've met the 51% rule. Just need a builder log to prove it was you.
https://www.sonexaircraft.com/aircraft-certification/I printed out the checklist and letter of eligibility for my kit in case the inspector wanted to see them, but IIRC it was a non-issue as he was already aware that it was an approved kit.
Also of note is this statement at the bottom of the checklist:
"► The applicants completion of tasks can be documented in a number of ways and may include
(1) Builder’s logs.
(2) Photographs/video/DVD.
(3) Drawings.
(4) Engineering data when necessary.
(5) Relevant documentation (e.g., plans) and references (e.g., handbooks) used.
(6) Documentation concerning any commercial assist
(7) Documentation concerning any non-commercial assistance used.
(8) Part inventories and histories.
(9) Receipts, Catalogs.
(10) Log book entries"