Can anyone tell me if they put build sheets in 66 Mustangs? If they did, can anyone tell me where to look?

 

Yes most every car had a build sheet put into the car. The build sheet was tossed inside the interior as it rolled down the asssembly line, many were put inside the seats, some under the carpet, some under the back seat, and i have even seen/heard of some up inside the dash. start with the back seat than the carpet, last i would tear apart the seat, only if you plan on recovering them

 

A common area folks have found them is taped to the wiring harness behine the instrument cluster. Another area besides what was mentioned in the previous post to check is in the doors.