Turbo charged 1971 Dodge Dart (Video added)

Absolutely badass ride man! Love it! Quick question on the rear end and wheels. It looks like it has been mini tubbed and spring relocated correct? I love the wheel and tire combo on the rear and I am looking at doing something similar on my swinger for when I take it to the track. I see you have listed the wheel and tire size, but I am wondering if you can tell me the backspace on the wheels?