Maybe and this is only a thought, since a couple people on this post with real 67 Sprints have already said their tag does not have the 3H on it, obviously 3H is not for Sprint. Maybe the 3H is for the side Stripe without the HO in it which could be ordered on any Firebird, I know the 326HO had its own Stripe. That would explain the 3H code on Firebirds built with non Sprint engines in it. Now if a 326HO car has a 3H then maybe 3H is not for the Stripe and maybe something entirely different.

Maybe someone who decifered these codes years ago with bad handwriting wrote down Stripe for 3H and someone else took it to mean Sprint, after all Stripe & Sprint are each 6 letters long, human error and then it gets printed and everyone takes it for being correct.

Someone should see if the 3H Firebirds had the side stripe marked off on their PHS.

Again this is only a thought and I have no solid info to say this is what happened.