I don't know about the OS 56 carb but the OS 52 carb is a direct bolt on swap with the ASP/Magnum FS52 and ASP/Magnum FS61 carbs. These carbs will also directly bolt onto the OS 48 four stroke.

I have a OS 56 venturi on one of my OS 52 engines so it is highly likely this carb will interchange also?

At one time I had a Magnum and a ASP FS61. They were identical except for the name on the side. Magnum only sold the 61 for about 6 mos back in 2001.