I've done with both my cars and my truck with Dynamat Extreme in bulk packs. I found it on sale on Amazon for about 1/2 off with free shipping. It is heavy. I do two layers on the wheel tubs, and one the entire floor, ceiling and doors(some strips inside and on the panel).

The key to insulating airplanes or cars is that products like dynamat are designed and are very good at reducing panel resonation, and not so much at reducing heat transfer. You actually don't even need to cover the entire surface, just use enough to stop the resonation of the panels.

For best sound deadening, heat and fume rejection, you must use a double sided foil covered insulating blanket type material on top of it. I get mine from Speedway Motors. Its very reasonably priced there.

I cocoon the entire interior from glass to glass with individually cut pieces that I tape together at the seams with that aluminum foil duct tape that has the peel off wax paper backing..I also do under the headliner, dash and doors.I tape down the edges just out of sight of the interior trim etc. By '70 E-Body sounds like you are sitting in a bank vault when you close the door. I swear it is as quiet as a Bentley rolling down the road. Most people are shocked at how much of a difference in terms of sound reduction/deadening and heat and fume rejection this technique provides. I learned how to do it this way reading about how they insulate small planes.