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The 70's proved that under then current rules, you could throttle all but the best of run games. If you wanted a best offense with a running game, it had to be in college if not the CFL.
So I think its an open question whether more 60s running teams could be considered for the best offense. Even the Packers running attack was being held in check later in their decade, both by innovation (Flex Defense, preponderance of 4-3 fronts) and by age (Hornung and Taylor).
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Think of the direction the NFL could have gone with to revive the running game (like they actually did with the passing game). Imagine rules that only allow two d-lineman on the line, only three linebackers max, and players having to be at least three yards off the LOS, IOW the unsound! Capers defense!