Hi,
If you look at
www.redbook.com.au you will find that WQ is listed with 1.6, Duratec, 74kW, while WS is listed as 1.6, Duratec, 88kW.
https://en.wikipedia.org/wiki/Ford_Sigma_engine
The Sigma article on Wikipedia describes the difference to be that the later revisions of this engine contains dual VCT.
With this in mind, it could be a common block and common parts, but the heads are different, so it wouldn't be interchangeable unless you also change over the management, harness etc, but that again wouldn't match with your vehicle electronics and so on.
Cheers,