What size were stock '73-4 Dart Swinger wheels?

With the proper backspacing fairly large wheels will fit, have you checked the "post your wheel and tire combo" thread...http://www.forabodiesonly.com/mopar/showthread.php?t=14254

Just glancing at it quickly, it looks like up to a 275 wide rear will fit. Might not fit everything, but you can figure a 255 would be a safe bet.

Typically on a stock car you can get 4.5-5" of backspace on an 8-9" rim before you start hitting the springs or anything else. Here's a page with a '69 Valiant that fit a 17x8", 5.6" backspaced rim with a 255/45/17 on the front, same wheel will fit the rear but requires a spacer to clear the springs...http://www.moparfins.com/CLAIRDAVIS/Cobra_Wheel.htm