The 268/284 cam was introduced with the 440/375 in '67 and expanded to the 383/335 Road Runner/Super Bee engines in '68.
The 256/260 cam was the "standard cam" for the 4bbls starting in '66 with for the 383s and 440s. Not a bad cam. The companion 2bbl cam was the 252 cam that went back farther, but was replaced by the 256/260 in '67.
The 383 and 413 and 426 Street Wedge V-8s had cams that were similar to the 256/260 cam, but with a little more duration, but not to the extent of the 268/284 cam. Seems like valve lift was about .431 and duration was about 260/268 on them, best I recall. But when I finally saw one of the log-style exhaust manifolds off one of those motors, that's about as much cam as they would tolerate--YIKES! Not too much worse than the manifolds on a '57 392 Hemi, though, but they still worked well, all things considered.
One thing Chrysler did was build engines with matched components. Meaning the carb worked with the intake that worked with the heads that worked with the cam that worked with the factory dual exhaust. A synergistic situation--something that GM and Ford didn't seem to do quite so well. Maybe a contributing factor to Chrysler's dominance of the Mobil Economy Runs back then?
The original 426 Street Hemi cam was solid lifter and a little milder than the more famous hydraulic version of about 1970 (284/284). Chrysler sources claim the later cam was worth an extra 10 horsepower over the first design.
By '50s orientations, when the design work was done, those were sizeable camshaft specs. No need for massive lift or duration numbers for a stock motor if the heads flow appropriately.
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