The Ford Car Parts book shows the same brackets are used for 1967 thru 1970, C7ZZ-6366740-A and C7ZZ-6366741-A, with the same hardware as used as well. These are service items. The 69 and 70 Assembly manuals do not seem to contain the fixed seat information. The latest information is from the 1968 assembly manual. Seat to bracket hardware: 382539-S2 1/40-20X1 1/8 pan head Phillips with an external tooth lock washer; 382547-S2 5/16 flat washer, 0.328ID, 0.750OD, 0.031T; 382540-S2 1/40-20 crown nut, locking. Bracket to body: 4 ea 382538-S2 1/4-14X3/4 truss head. Somewhere in this time frame the government required certain critical hardware items to be color coded, like seat hardware, hence the red nut.
Jim