I used M6 rivnuts and black button head hex bolts to attach the upper panels so they could be taken on and off if needed. The lower panel is riveted on. For the ones in tight corners of the frame, I used the nut and bolt trick to insert the rivnuts since the large rivnut tool would fit. This method is kind of a PITA, but it worked. I used adhesive-backed thing foam weather stripping between the rivnuts to keep the panels from vibrating against the frame. They sound very sturdy when you tap on them even without sound deadening which I will add on the interior side later.
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The finished firewall installed. I will make cutouts for wires, fuel lines, shift cables, etc. later on. I think it came out pretty good and it looks awesome on the car.
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