Not sure what "legal" means, but...
1. is the aircraft currently flying and does it have an "N" number.
2. look for the data plate on the structure of the aircraft.
3. Look for the FAA registration paperwork that need to be in the aircraft
4. Look for the FAA airworthiness paperwork in the aircraft
5. look for a weight & balance document in the aircraft
6. be sure all paperwork (items 2-4 above) references the same N number as in #1 above.
You can look on the FAA data base, search on the N number, and see what the FAA knows about the aircraft.
If the aircraft has not been previously registered, search this site for a wealth of information on what is needed.
As others have added, the Operating Limits are required to be in the aircraft. It should specifically call out Phase II. (Once the Phase I is completed, there needs to be a signed entry in the Airframe Logbooks stating the fact, and then the Phase II Op Limits apply. The Op Limits become a formal part of the Airwortheness Certificate, and as such, must be carried in the aircraft.