Hi Matt.
If they are Kodak Prints, they may have been printed on:
Kodak Ektacolor 20RC paper Type 1822, introduced in 1968 or
Kodak Ektacolor 20 paper Type 1870, introduced in 1967. 1822 was 1870 on an RC base. 1822 was the first color printing paper in the world on an RC base. Ektacgrome Paper was RC based in 1969, Agfacolor paper was RC based in 1972 (MCN310 Typ 4)
or
Kodak Ektacolor Professional Paper, this was on an ordinary paper base.I think the other two papers are more likely.
The paper, whatever kind, would have been processed in Kodak "Ektaprint C" chemicals at 85F. Process time around 22 minutes.
P-122 was not around in 1968, (unless there were some Retro labs in the USA!). P-122 was superseded by Ektaprint C in 1965.
Ektaprint C was a five solution Process: Dev, Stop-fix, Bleach, Formalin Fix, Stabilizer.Washes in between.A five solution process called P-122 was around in the UK in 1963-65. This became Ektaprint C in 1965.
If they are on Agfacolor paper, (from masked negatives) they would have been printed on: Agfacolor paper MCN111. Process time 30 minutes at 68F or (unlikely) process time 17 minutes at 77F.Times varied a little at the higher temperature.
MCN111 was introduced in 1963. There was another paper called "MCN111 Typ7" introduced in 1968 (rolls only, sheets in 1969). Don't I remember!I was a photo color printer in those days and must have made thousands of prints on MCN Typ7 and on the improved version MCN111 Typ4. All the best MT