I don't know if it's set in stone, but I think the older motors (i.e. pre 70's & maybe early 70's) have adjustable rocker arms so you don't just torque them down. I have a C8 (1968) engine code, and my rocker arms are adjustable. Easiest way to tell is to look at the rocker stud. If the threads of the stud are the same width as the unthreaded part, then they are adjustable. If the stud has a shoulder, meaning the threaded part is thinner and the unthreaded part is wider, it's not adjustable and can be torqued down to spec.
As far as the rocker arms being loose, it might just be lifter bleed down as mentioned earlier. Typically, the lifters/rockers on the low side of the cam will loosen up (bleed down) when the motor is not running. If they really were loose, you'd probably hear some tapping when running. If you're not familiar with that tapping sound and you're really curious (for adjustable rockers), you can loosen a rocker nut approx 180 to 360 degrees while the motor is running (just remember how much you turned the nut so you can turn it back the right amount).
