It's not that cut-and-dried. For example, when you say ".46 two stroke", do you mean a O.S. .46LA or the .46FX or later AX version?

As a general rule of thumb, two stroke displacement X 1.5 is a pretty close match unless the two stroke is a plain bearing economy engine like the OS FP or LA engines or if the four stroke you plan to use is a YS with built in supercharging.