On the set of “Spinal Tap II,” Rob Reiner is doing double duty: directing the movie while also playing the director on screen. 60 Minutes was there as the filmmaker repeatedly switched roles. “It’s making me nuts!” he says. The new film is the sequel to the cult classic, “This is Spinal Tap,” released 41 years ago and often ranked as one of the funniest films of all time. #spinaltap #onset #robreiner