My stock 1955 292 has been modified to 12 volts, '57 distributor, '57 "D" code manifold and new 465 cfm Holley.  It runs and drives fine.  I have a set of "G" code 1957 Heads that just returned from a new valve job. I also rebuilt the high ratio rockers from these heads.   I also have a set of 1957 Exhaust Manifolds from the same engine.  My plan is to swap the '57 heads and rockers on to the '55 engine.  Will I notice the difference?