Just been given my MCK for a G19 built from the poly80 kit that has a custom Rock fluted slide and threaded barrel. When ordering I was involved whether the extra 50 % inch of your threaded barrel would fit once the barrel shroud was extended to G17 size. Ironically https://glockstabilizerkit41851.angelinsblog.com/25831133/about-recover-tactical-20-20