While I thought 4P was for Fisher for body reinforcement, I'm in a Camaro group that is trying to state 4P was determining SS in 67. I've read the CRG articles and all the discussions I could find. But 4P on the tag predates the actual installation of the traction bar upgrade that was in December 66. So what was actually the reason for 4P on the tag when it was on SS350, and Z28 and eventual mid year big block.
