On my 70 Cuda, I have stripped the interior and underneath the car with an electric angle grinder and wire discs. A cheap wire disc (about $4 each) will very quickly strip about 10 square feet of car down to the metal. Last weekend I completely stripped the interior (roof, floor, firewall, rear) in less than 3-4 hours. I then wipe everything down with acetone and usually use etching primer. Corners may require chemicals or a dremil tool with wire brushes or some selective minimal sandblasting.

The photo here shows about 20 minutes of work in a wheel well. You can see the wire wheel went through dirt, undercoating, paint and primer like butter.

I prefer this method because its cheap and fairly quiet. HOWEVER, you must protect yourself because those cheap wire discs will fling metal spikes as they wear and they will penetrate skin so cover your eyes with good goggles and protect all other skin with thick clothes. Also, if you are in a confined space, keep a fan on you or wear a respirator since you don't want to inhale any of that crap.

Here is a link to the knotted wire discs I was talking about. I also have plenty of photos of my interior all stripped down from last weekend.

http://www.amazon.com/gp/product/B00B21CH7A/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1