If you want to use the Ford Biscut (cushion?) mounts I would reccomend the Chassis Engineering Inc mounts (actually a different company than Chassis Engineering). They are rubber over steel so they don't move much, but will damp engine vibration. We fabbed brackets for our Anglia out of 1/4" plate (cause we had it). If we had to buy the metal it would have been 3/16" or 1/8". I don't have a picture right now, but just make sure you gusset it fully. The only piece that needs to be a specific thickness for these is the piece the tin plate part of the mount goes through. It needs to reach through fully (as close as possible) without sticking through the other side.
http://www.chassisengineeringinc.com/page5.html It's the shiny piece next to the bolt on the left between the upper and lower biscut.