BillGrissom said

It looks like you already have 2 holes drilled for a later 2-hole aluminum MC. That is what I did for a manual MC in my 64 Valiant. I just used a big washer to cover the opening. I wouldn't fool with welding a plate to the firewall. Just wirewheel the rust off and paint. The pedal load is mostly taken by the brake bracket under the dash. If you use DOT 5 brake fluid (silicone), your paint won't disappear again.

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