Super -6 is a misnomer! It really is a WHAM-BAM, THANK YOU MA'AM pocket rocket, with 300 HP!! It accelerates like a carrier launch and cruises at VNE!! Climbs approach 3,000 FPM
They add around 8" to the cowl to accomodate the Lycoming 6 cylinder and so, usually add 8-10 inches to the rear fuselage for CG purposes. Usually the tail surfaces have thicker skins as well.
The wings are shortened by one bay but all the ribs are used, just spaced closer together.
I believe that there are a half dozen or so flying.
Kahuna, from Atlanta, flies a Super -8 that he built....also IO-540 equipped.
Truth be known, John Harmon started this by shoe-horning an IO-540 in a -4 and it became the Harmon Rocket. Various iterations followed.