1968 Airbox rebuild question

I took the non-AC airbox out to rebuild over a year ago and finally got to it this week. My question is about the 2 black metal plates for the heater core tubes. One is larger with larger holes centered in the plate. The holes of the smaller one are offset, closer to the top, or bottom, as the case may be.
1. Which of the two screws to the inside of the firewall?
2. For the other one, does the plate go inside the box, or on the outside where the tubes come through?
After consulting several books, including the shop manual, the internet, and YouTube with no luck, believe me, any help will be very appreciated. I've got to back and epoxy the cracks I've made. Thanks