With the tri-power 389 engine the oil filler cap should be on the passenger side of the engine. I can see no advantage myself to relocating it to the left side unless someone here knows of any particular reason?
I agree with 67GTOCoupe. Every one I've seen are on the Passenger side.
1967 GTO, 400 RamAir, 4-speed, Frame off, Quasar Blue Metallic, Edelbrock Performer Manifold, 650 Quick Fuel Carb., Pertronics Electronic Ignition, Crager S/S Mags.
WNY Pontiac ( POCI Member)