On the 1967 B-bodies, if you ordered the Hemi with a four-speed, power disc brakes were a mandatory option. If you ordered the Hemi with the Torqueflite, there were no braking requirements. This as per the salesman's pocket reference.
Are you sure about the info in the above post? Please show where is says that hemi 4 speed requires disc brakes.
https://www.hamtramck-historical.com/dealerships/1967SalesmansPocketGuidesPlymouth-01.shtmlSee photos, from salesman pocket guide.
GTX is far right column.
HD brakes standard, disc optional on all models.
Looking on transmission, engine and brake sections, nothing about this as mandatory.
451 is power brakes
408 is sure grip, they have those down as required.
I have the 1967 data book and reading through it about brakes, transmission, and hemi there is nothing said about this combo requiring disc brakes.
