What are the chances that the fellows in Spinal Tap (Christopher Guest, Harry Shearer and Michael McKean) saw this before Spinal Tap and were influenced by it?

Check out the drummer and bassist in this Boston video. ( 0:45 and 1:35 marks) Totally Spinal Tap! Also, is Brad Delp (the singer) a twin of Doug Henning? But man would I love to be able to sing like that…