So, it'd be considerably more helpful if you would've taken a closer photo of the headtube and headset rather than a low resolution photo of the whole bike.

If the headset cups recess into the frame but have a lip external to the frame, you need a zerostack for a 44mm headtube headset like the one you linked to. From the photo it's reasonably clear it's not an external cup headset. If there are bearings slip fit directly into an integrated cup, you need a IS headset. Also headsets can have a mix of any of the three common headset types.