............ None of the Fisher codes on a trim tag directly identify a specific engine or drivetrain component, they only identify extra work that was needed to be performed on a "base" body to prepare it for the drivetrain and other options to be installed by GM on their side of the plant. 4P just mean't that Fisher needed to install the front bracket for the radius rod, that GM would install later.
Based on your comments above, why are there specific 4P thru4 L option codes listed that do define an engine option (section 4) and tranny option (section 2)?
As for the radius rod, I suspect that this may not be an engine error based on the CRG report for radius rods that states:About one-third of L48/M35 cars have been noted with the round radius rod installed, while the remainder have the rod brackets but are absent the rod. No definite installation pattern has emerged
I have to say that this particular car research is interesting indeed.