Well, This is a bit more tricky then I thought. The hole size that I ended up with is 9/16"
but I did not have a drill bit that big. So I dug out my unibit and went to work. Well, It opened the hole nicely, but the material is so darn thick that you can do it in one shot. altogether.
I managed to accidentally go too far in the right T-410 reinforcement plate.
.
The hole in the left T-410 reinforcement plate was just off a few
thousandths. I guess when I took the assembly apart and upsized the
holes from 1/2" to 9/16" it ever so slightly was off center. So I decided to fabricate new reinforcement plates. The left one could have worked just fine, but since I needed to make a right one...It was easy do again.