What holes do I need in firewall?

[hpcgmc]

I've got a welder who is VERY slowly repairing the rust in my cab. I decided to remove the heater box and replace it with a vintage air heater (eventually vintage air a/c). Since I'm having the welder fill the heater box hole, I decided I'd have him fill all the unnecessary holes in the firewall.

When I got to the driver side, I couldn't recall what went where (cables, wiring, rods, etc). Here's a couple pics. Are there holes in the firewall from the factory that I should be filling? There are a few holes on the firewall above the bellhousing that don't seem to be necessary.

Any ideas?

Thanks!