What is this stuff. It looks like a heavy rubberized (sort of) mat glued on the rear firewall. My guess is sound proofing but am I right. More to the point does anyone reuse it or can I stop trying to take it out without ripping it?

Thanks,

That's exactly what it is. Some people keep it and others don't. I pulled it out of my last car and left it out.

Can you buy reproductions of the original anywhere? I looked on Pelican but they only seemed to have a new fangled silver one. I haven't decided what my end goal on this car is but I know this will probably have to come out to do rust repair

I don't think there are originals or reproductions of that piece. If you think you may need it, remove it carefully. Heat would help.

It weighs a ton. Trash It!
and let the sweet sounds of the motor serenade you while you drive.