OK, I measured the driver's side one and it's about 4 inches left to right and 5 inches front to back. IMHO, the shield should be more like 6 x 6. Shortly after I replaced the mounts, I spilled fuel all over the left mount hooking up the prefilter. The fuel easily splashed over the shield and flowed all over the mount. I quickly washed it off, but realized that shield is almost useless for deflecting a fuel spill.
I went to measure the right side shield and there wasn't one!
Then I remembered how I left it off when I put the engine in because I wanted to straighten and paint it. I forgot to go back and put it in. Now, I'm tempted to just make up a pair out of copper (because it's so easy to form) that do a really good job.
Rob, I suspect you'll need to form that same type of recess in the top of the shield before you make the bolt hole. It's about 10-12mm deep, the small ID just clears the OD of the aluminum engine mount and the OD of the recess is about 35mm. Looks like you could make that by squuezing your shield between 2 different size sockets.