[johnta1]

1st it seems you probably have all BHC's (billing history card) since your cars are older. They did give the actual engine code and rear end info plus other things.
The later PHS' like from 1968 to about 1977? maybe were the ones I'm familiar with and most here are probably familiar with.
They did not give the actual engine codes or rear end gear info. It is 'implied'.
Certain codes were used for models, so if it was an upgrade, it would show the upgraded sales code which PHS would highlight on the extra sheets.
This would have certain codes which would determine what it came with.

The late PHS' were different than the previous ones.

Here is a copy of a 1980 Firebird. (not mine)





That is why I asked for yours.
We could explain the info and probably answer everything you need.