Just finished my Semroc X-21. The build was fun and challenging. The quality of the Semroc parts was superior as usual. The hardest part of this build was interpreting the downloadable instructions(pdf). The Semroc CC kits don’t include the instructions but give you a link to the downloadble plans. These are the original Centauri plans and require reading a few times before attempting the build. This thread at the Ye Olde Rocket Shoppe Forum is also helpful.Read and pay close attention to the diagrams and you will enjoy this build as much as me. Here she is:

x21