well, a stock rim is 4.75" backspacing, 15x7" if you are widening, you want the clearance to remain similar.. sooo if the new rim is 9", with 5.0" backspacing, you need 1/4" of spacer, maybe. easiest thing I can tell you, take a board/ruler/anything with a flat edge long enough to sit on the rim. set this down on the BACK side of the rim, using a ruler/measuring tape measure the distance to the plate where the lug holes are. any distance OVER 4 3/4" will require the difference in spacers. Measure your distance from center spindle to outer most extremity (usually brake caliper) multiply times 2, and measure the distance from the spindle where the lugs are back to the forward and outer most extremity on the spindle/brake assembly (usually the caliper also)
that much room must exist between the outer edge on the BACK side to allow for the wheel to not have clearance issues.
Most of the wheels you've shown have inset lugnuts, so its likely you will have minimal issues, since the front of the wheel means nothing, its the distance of the mounting surfaces that will make issues.. if you are putting a 17" or 18" wheel where once a 15" wheel resided, the likely hood of offset being a major issue is slim, since you have more room on the inside edge in MOST cases. if the rims outer edge is abnormally thick, this statement might be wrong. ...
If you can't find the backspacing of the rims, troll some Mustang forums, its probably been asked 1000 times, so it should be easy to find!
good luck!!
If you also keep in mind you may loose turning radius, then the larger rim may be farther back into the wheel well as long as it clears things like Tierods and so forth.