Match Race ~ 1970 'Duster 340' vs. 1969 Mustang 'Mach 1' 351W

I didn't think they started retarding cam timing until '72 or so, for emissions. Did they do that in all their engines, or was it just the 385-series big blocks?

I've seen cams retarded in 289s as far back as 65. Ford was famous for it.