I have a brand new OS 46SF about to go in my 2nd Dazzler. I never knew I had it. I bought it in the late 80's. My first Dazzler has OS 46FX that is over 4 yrs old and has turned into my all time favorite engine. I also have a NIB GMS 47 2000 that I may switch with the OS 46SF. The mounting holes are identical. In looking at the instructions of the OS and GMS, it would appear the GMS 46 (Now the Tower 46) is identical to the OS 46SF. The bore is 19mm, the sroke is 22 mm and the cranks are the same length. The bore was increased from 19.0 to 19.2 mm and they called it the GMS 47. I have heard that most all the 46 size Chinese engines are clones of the OS 46SF. This includes the Magnum, TT, GMS, and ASP.