Best and easiest way on a modified car is to forget the firewall pad. Instead insulate the firewall with Dynamat or whatever clone you prefer - both a sound and thermal barrier is preferred. Then just run the carpet up to where you can't see the edge of it. That can be one piece custom or a second piece above a pre-cut carpet.

This gets you 3 things. First is the stock firewall pad fasteners are at best frustrating and they don't look so great on the engine side. Second is better insulation. Third is it looks better. Obviously it won't look original.

 

Good idea ... doing that on the Vette ... :tu
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