I'm willing to bet that the 3H is NOT the code for the Sprint package at all.

Like many things in reference material, it was probably written wrong once and since then it's been taken as correct.

I have a 1967 Firebird Sprint, with PHS, with no "3H" code on the trim tag. Lucky for me, there's no 3F code either. I'd hate to think I might have a counterfeit Sprint on my hands made from a garden variety 400.

I hate to tell you where I pulled this from. It's also an opinion, but it sounds like a valid one:

The complete original Fisher factory documentation for these codes is not in circulation - if it still exists at all. Nevertheless, a large number of the code meanings have been confirmed via a Fisher production form called the Uniform Option Identification Tag (UOIT) that was sometimes carelessly (but fortunately, for us) left in the car during build - often under the carpet or inside the headliner or in the springs of the lower rear seat. Those codes that have been confirmed via available UOITs are so noted - and the exact wording of the UOIT description is shown in monospace font. The remaining codes have been decoded via statistical analysis, and are therefore not known exactly, but by inference.

Those who have a 3HF code on your trim tag should pull the build sheet and look at what it says.