I had a toy back in late 70s or early 80s that used rubber rivits to hold panels and parts together. The "riviter" was a tool that grabbed the head and stretched the body of the rubber rivit so it would squeeze through the holes. I think you need that tool.
68 Road Runner (383/4speed, post car w/decor pkg) - Major Project 69 Road Runner w/472 Hemi & 4 speed. 70 Challenger R/T SE EF8 w/ V9J, U - A32 - Major Project 2023 Ford Mach 1