I worked from home today and cooked some food to take into work tomorrow for the staff at the office - the WSM performed magnificently with the Weber attachment, that arrived this morning.
I found ou can wedge the foot under the clip and above the screw, it seats perfectly and doesn't budge. As mentioned earlier, the horizontal bars do come off too easily if the hooks stick them, I quickly got the 'hang' of twisting the hook a bit to unstick it. nest time I will tie them down with a bit of wire.
I'm amazed at how well this setup worked, I made my own Montréal chicken seasoning (I toasted the coriander seeds first, made a noticeable difference!) and hung the halves with the probe at chicken level reading 250°, and brought the temperature up after a half hour.
An hour and half in they were perfect, skin crispy, juicy, and looking amazing. I ate the backs and some sausages I hung at lower heat after pulling the chicken off, for lunch, they were off the charts delicious. I put a potato on the probe and it was so perfectly cooked and fluffy after the chicken was ready I realised I should have improvised something to cook some more of them- next time I will buy some flat shish skewers as recommended and put vegetable and potatoes on when cooking higher heat like this again.
It took me no time to get the hang of cooking this style, and it opened up the possibilities by 100% for me. I had no trouble getting the WSM up to 300° at the end using lump charcoal.
So thanks all for the tips, it made everything so much easier!