I was looking at a 69 and the trim tag had NO28 in the spot where is usually has the x code. Anyone know what it means. Thanks

That would be from a Van Nuys car and it was an internal plant code. Nobody has the records to decode them. The Van Nuys cars didn't use an X code, the Norwood cars started using the X codes around the middle of December of '68.
Hope that helps,
Doug

So without a build sheet there is no way to tell if this is a true "Z" car? The orginal moter is gone so we can't go by that either.

Correct. Without a chassis broadcast copy, protectoplate or some other kind of paperwork there is no way to prove what a Van Nuys car was originally.

There was some discussion here recently about the M21 and the only small block car it could be ordered in was the Z/28. So if you have a small block heater blower motor box and an M21 with a matching VIN it could be an original Z.
Doug

http://www.camaros.org/diffs68.shtml