Hey !
Here's my experience with a Cessna 150 that still isn't registered after 4 yrs of trying (late 2017). The problem was that it was declared "scrapped / destroyed" in the FAA de-registration paperwork before I bought it. The FAA considers it non-existent. I have the airplane, airworthiness cert, data pale and logs. As Bruce said, they wanted photos of the complete airplane, but it had to be full assembled. Following the rebuild, I sent in the assembled photos in 2021, but during the rebuild period, the rules for FAA Order 8100.19 changed in 2018 to require a written plan of repair to be approved by the local FSDO and submitted to the FAA registration branch. I got the belated repair plan approved and submitted, but they're admittedly 4 mos. behind in all of there registrations.
And on top of that, the new registration number I applied for 2 yrs ago will not start to be processed until the airplane registration has been approved under its original de-registered N number. Another 4 mos ! Egads !