If you've got the 73+ disc brake suspension in front, the way you get a 17" or larger wheel with 5.7" of backspace to fit is to...
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... bolt them on. Of course you have to make sure that the center bore of the wheel is Mopar size, ditto for the bolt pattern, and shoot for a width of 8" or less. The limiting factors for fitting large backspace wheels are the outer tie rod ends (OTRE's) and the upper ball joints. The UBJ is the limit on wheels below 17", and the rule of thumb is 14 & 15" wheels can usually tolerate up to 4.25-4.50" of backspace; 16" wheels can tolerate up to 5.0", and 17" wheels can tolerate up to 5.5" of backspace. An 18" wheel is pretty much up and over the UBJ so you probably don't have to worry about interferance there any more. Always check, though.
Typical 1994-2004 Mustang wheels have about 5.7" of backspace, and lots of folks (including myself) use those with great success. However, some folks with otherwise identical suspensions can't tolerate quite that much BS, so a thin spacer might be required to clear the OTRE. Again, going to an 18" wheel MAY get you around the OTRE so you MIGHT be able to run really big backspace - like 6.5" or so, and allow you to tuck 9" wheels and 275 tires under the front end. You have to do LOTS of measuring at this point, and you have to pay close attention to how the wheel is actually constructed. I've got a high-offset 18" wheel that won't clear the OTRE because the forged wheel rim was spun with a strange drop in it so right where the OTRE wants to sit, the wheel acts like a 17" wheel. Rats.
I also know that a 245/45-17 fits great up front, at least on my 69 Valiant. It's close to the rear outer fender bolt, but a panhead bolt would fix that easy. I HAVE fit a 275/40-17 up front on the same 5.7" BS Mustang wheel, but a tad more BS would make it fit better. Ditto for the rear - where I'm using a 65-67 B-body rear with relocated A-body spring perches. On a stock A-body-width rear, you'd need about 3/4 to 1" of spacer to make the Mustang offset work.
Oh, and I like #3 as well. Nice and clean, and it looks light, too. Any idea what those wheels weigh? Among those three choices, I'd choose the lightest and go from there.
Clair