The fuel vapor seperator was moved from the passenger trunk area to the axle kick-up area just forward of the fuel tank so the hoses no longer needed to pass through the frame.. The holes weren't punched on 72 & up...

Quote "I believe they phased out the trunk tube system about the time they implemented the charcoal cannister/vacuum hose deal."

Not entirely correct the Fuel vapor seporator is still used, just redesigned... The charcoal cannister actually replaced the Engine Crankcase as the location to store fuel vapors...