I just installed mine last month, once bolted in I noticed the same problem I adjusted the up stop so the horn just cleared the lower edge of the bulkhead, slid the stabs back on leveled the plane made the jig and checked the neutral and full up position which in my case a 59 250 is 13 degrees
+ or – 1 degree was within spec,the down limit was fine, checked balance everything good. The Aussie horn is thicker than the Piper Cast horn and the opening in the bulkhead must vary slightly.
Fred