Welcome aboard! Well if it is a Norwood, OH built car, the z28 or 28.19 should be there as you mentioned. If it is a Van Nuys, CA built car..I believe this info is omitted from the trim tag. It seems strange to me that a Van Nuys car would've been originally sold at Yenko but then again, I have absolutely no idea how the dealers got their cars. There are a couple of other things to look for for it to be an original Z (although most are fairly easy to fake). The gauge cluster should include 150 MPH speedo and the tach should show the redline starting at '65' or 6500. According to what I've found thus far, all 70-71 Z's also had a floor mounted gas pedal. *see attatchment for these*. By default, all Z's were equipped w/ rear sway bars also. This should be easy to spot if the upper mounts on the rear frame rails, just inboard of the shock mounts, looks to be an original weld or added later. *The sway bars were also a part of the F-41 (?) suspension option, therefore not exclusive to the Z. Recently, a son of a plant worker at the Norwood plant turned up a huge number of 'in factory' build sheets.
partial list of '70 Norwood build sheets
...I'm not sure if he's done adding all that he has but so far I didn't see a match for you. Another great source for info:
2nd Generation Camaro Owners Group (2GCOG)
Check the decoding link on the front page...there's a wealth of info there.
Good luck and welcome to the forum.
-Mark Holman