Looking on my price list from Husqvarna, that mower is currently available with both the Kawasaki engine and also the Honda engine. I personally have only carried it with the Kawasaki. The straight push model, no drive, is a WC21 and is only available with the Kawasaki. The drive model, WCS21, and the model with the blade brake clutch, WCB21, are available with both engine options. The only differentiation between their model numbers is the honda engined one adds an H to the end of the model, ie. WCS21H and WCB21H.
In the 2010 Husqvarna catalog you will find them on page 122 but they only list it with the Kawasaki engine.