I think it would simply fall under the requirements for
any amateur-built EXPERIMENTAL aircraft. These are for the USA, don't know what they are for other jurisdictions.
https://www.faa.gov/aircraft/air_cer...ert/experiment
As to a placard or data plate, I suspect trying to use an official Cessna one would
not be a good idea. In fact, Cessna's lawyers would probably demand that the final aircraft make
no reference whatsoever to Cessna.
There do exist special EXPERIMENTAL data plates for homebuilts:
EXPERIMENTAL AMATEUR BUILT AIRCRAFT
Model: (say) Airfoil1 X52
Serial No: AF100001
Date of mfg: 17/9/2022
Engine: (say intentions)
Empty Weight: (weigh it)
Gross Weight: (test it)
Horsepower: (say intentions)
BUILT BY
Name: Airfoil1
Address: ------
City/State/Other: Stoke-On-Trent, UK