The instructions I used to get into a WD are as follows -
Bachmann WD Access
To assist with gaining access to the interior of the WD 2-8-0 locos, as well as removing the screw above the front bogie and the one under the cab, you also need to remove the centre screw in the keeper plate moulding. Then, after unclipping the handrails, the chassis can be carefully levered out.
I've followed the instructions twice, initially to put in a TCS decoder, then to replace it with a Loksound one.
Best of luck
Tony T