Rear Engine Fire Wall Rivets missing or broken

[Skymaster337B]

Attached is a pic of the rear engine fire wall, under the muffler, where I found rivets either broken or missing. The parts manual doesn't list any specific rivets for this assembly. Any ideas? The whole fire wall doesn't seem to be a load bearing structure. Has anyone ever experienced this before? Or even better yet, check your airplane and let me know what it looks like.

[skymstr02]

I don't have my structural repair manual handy with me right now, as I'm sitting at gate A8 in Memphis waiting for a connecting flight to St Louis, but I believe that those rivets are monel.

Just because monel rivets are difficult to shoot, I think that if that were my plane, I would order monel cherrymax's from Spruce. Go for the oversize ones as the holes are likely to be elongated at this time anyway. The grip length is probably a -1 or -2, but check it anyway to be sure.

When drilling out the old ones, it would be best if you could use a drill bit lube like Boelube to keep the bits from wearing out too soon. Don't let the old rivets spin in the holes as this will wear out the rivet hole.