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The 265/70/18 is 32.6"s tall and 10.4"s wide, The 265/60/18 is 30.5"s tall and still 10.4"s wide. The tire will shrink by about 2 inches, but not get any skinnier. Hope this helps
Not too mention it might not look too good either.
... unless you're lowering the truck. You'll obviously need to recal your speedo too. Like you said, ride may be a bit more stiff with the shorter sidewalls... but those aren't exactly low-profile tires either.