Get some aluminum flat bar like below.
http://www.homedepot.com/p/Everbilt-1-2 ... /204604762Also while you are picking that up, get some black heat shrink to cover the aluminum flat bar once you have sized it properly. You may want to bring some of the screws from the WS420 with you. You may need to pick up a set that is a little longer to account for the thickness of the aluminum flat bar.
If you would like visuals, I could probably get some pictures of mine this evening when I get home from work.
