Opinion: Using logic and the fact that no one has seen a pic of a pan or non wiki literature.
Don't think rivnuts were used back then on GMC trucks. Too bad about the phone. Probably a previous owner add on. Or some upfitter. Never seen mention of an option for that. No RPO.
Pan could interfere with designed airflow. No practical reason for it. No reason for a blind fastener application.
If it was an option, rivnuts would be seen on 4x4's trucks that didn't opt for a pan. Usually provisions for options were already on the piece part at subassembly level. Must be a radical shape pan to fit around the deep bend in the tubular cross member?
Installing rivnuts and a screw cost more than just a screw. Let us know when the new phone is worked out. Glad to see any actual link to a post anywhere. I will be the last to admit I'm wrong.
