One of the first things that got yanked back in the day to get more fresh air into the motor to try to get more performance. Was cheap, easy and did not cost anything and is when 90% of the screws got tossed out or lost. The rest vibrated out on there own and got lost.

Pan head phillips #6 X 1/4" long black oxide or something dark. Might be a 8 but pretty sure it's a 6 without researching the screw more.

Looks like a 8 in the pictures but in real life they are small.