Anyone put a fuel cell in a 64-66 Cuda? Bad idea? Fumes?

You could step down the mounting surface of the pump, or create a hump in the floor with an access door.

Or...contact those guys roccodart440 mentioned and see if they offer something that fits your car.

Here I spent 2 minutes Googling and found your answer:

Fuel Injection Gas Tanks

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Yeah, in my original post I mentioned the Tanks Inc EFI Tank as a route I may go.