My Ryobi 31 is a 2-ring, short shaft engine with Paragon motor mount, prop shaft, prop hub & Jag muffler. From firewall to the rear prop face is 7-inches. Don't know how Jag muffler works with smoke but outlets can be rotated 360 degrees to position as desired. Has Frank Bowman rings, about one hour run-time & turns 7400-7500 with 18x8 MA classic prop. Has manual choke but use standard electric starter without choking.