Projects Smoothing the firewall: body work questions

I have been working on the firewall of my 50 chevy deluxe to fit a 350 small block. I've removed the fins, plug welded most of the holes and ground it all smooth. The problem is now the metal is a little wavy from the heat and torture. So my two questions are:

1. Can I use a thin coat of bondo on the firewall to smooth it, or will the heat from the engine be a problem?

and

2. When I paint the firewall, do I need to use a high tempature paint or will plain old rattle can satin black be okay?

Please be gentle, I'm new to body work and this is my first frame up car build. I'm learning as I go. Thanks

 

i have put plastic filler and regular paint on plenty of firewalls without a problem.

 

Mud and paint no problem.

 

Prep it like any other body work and normal paint will work fine on a firewall

 

X-4

 

Awesome, thank you all for the quick responses!!

 

Finishes like everywhere else: