Smoothing my firewall

[gtotto]

Hey guys,

I've searched the site (and others) for info on smoothing firewalls and found alot of different opinions and methods. I think I have come up with a solution and would like to run it past you guys.

I have a 65 GTO/clone factory A/C with several large factory openings in the firewall. I am planning on running an aftermarket A/C unit so the factory openings will no longer be needed. I could patch the holes and fill the dimples with filler but my main concern is the long, curved, horitonzal seam that runs the width of the firewall. I am afraid that if I try filler or weld on the long seam it may eventually crack and that would be bad.

My plan is to template a sheet of steel to use from the passenger side to just past the vin plate. This would cover up 90% of the seam and the wiper motor and brake booster would hide most of the rest. I was thinking 16 gauge (too thick??) and attatching the panel with adhesive on the low spots and welding the perimeter. I would probably drill a few holes in the panel before attatching it and then plug weld them.

Any input would be greatly appreciated

Thanks
Ken