Bruno was extremely dirty fighter. Also he held much, and had decent skills. It may help Bruno, but in the later rounds Lyle finally catches him and knocks him out like Smith and Witherspoon did.
This is no mismatch. Bruno would have been a serious threat to Lyle. I am a Lyle fan, but his accomplishments are not greater than Frank's. They are about equal there, in my opinion. Lyle may take a better punch though, which is why people are picking him, but this would be no cakewalk. In fact, I think it would be a brutal war.
That would be up to Ron, a guy who chose never to stop an opponent in the opening round as a professional, but always felt him out, part of his volitional objective to make up for a late start to become as good as boxer as possible. (It's why he made the crazy decision to take on Jimmy Young twice. It seems insane, but from Young II Ron took a 12 round SD from Bugner, and a ten round MD from Stan Ward following his 12 round tutorial from Professor Young. It paid off. Between 1971 and 1983, a span of 28 bouts, only prime Ali 2X, a well conditioned 208 pound Frazier coming off Foreman I, and Lyle were able to decision Joe Bugner, and Ron handed Stan Ward his first defeat. Stan was "only" 8-0-2, but enough of a headache to already sport wins over Jeff Merritt, Mac Foster, Jody Ballard and Kevin Issac. He would also rebound from Lyle with a decision over Mike Weaver.) My guess here is that Lyle would do what he did about ten times in his career, let Frank get warmed up in the first, then take him out in the second. Ron tended to box boxers and slug sluggers. Bruno's not the kind of opponent Lyle will be looking to go to the cards against.