I put in 9 1/8 dowel pins around the perimeter of the firewall on mine with a ys-120 and even after 50 flights still no problems. It took about 5 minutes to complete the modification. I also pinned the landing gear. The only problem so far has been a torn off elevator counterbalance when dipping the tail in the lake at my buddys farm. A little glue and some packing tape and we were back in buisness. Now I know why it was a good idea for the bolt on horizontal stab assembly.