You are correct about Glenn, but it was the same company, corporate office in Appleton, WI in beginning. Glenn Mullen, Bill and Bob's dad CJ ( a truly great man), Jerry Wood and Carl Bush were the owners when I first worked with them in early 80's, was a customer of theirs before that starting mid 70's. All class acts.
Bill and Bob's uncle and cousins had a separate construction company, Mullen Construction. They are the ones who invented the Mullen bender, which I'm sure some of the old dawgs on here used in the past.