A bunch of hardware / body plugs and other misc are on a couple of pages in the EPC. I don't specifically know where.

This part is a plastic hollow bolt and is probably used across all models in near by years.

I think the stud sticking out of the firewall is a standard 6 mm thread so a washer and but would work fine just don't tighten it all the way ( or use a self locking or MB factory plastic nut ) . The original hollow bolt bottoms out on the stud before it pulls the hush panel tight, this is to allow for dimensional variations.