['ol Pinion head]

'67-72 GM A-body disc brakes will not fit on '68 & earlier GP'S which were built on B series chassis.

For easy fit discs for the '65-68 GP & '65-70 Pontiac B series, one would be best served using the single piston caliper disc brakes off a mid '68-70 Pontiac Bonneville, Executive, or Catalina. This set-up is only the same on Pontiacs. Buicks, Chevys, Olds, all used their own specific spindle, rotors & calipers on the pre '71 B series disc cars & will not swap between other lines.

Most importantly, make sure when sourcing the used Pontiac rotors for this swap, that one finds THICK rotors with such a set-up, as the rotors are not reproduced, & are near impossible to find. These rotors actually fit back through the '67 Pontiac B series 4 piston disc set-ups. Though the '67 through mid '68 Pontiac B series used 4 piston disc calipers, & even rebuilt, one will often have problems with them. Good luck on your search.