245/45/17 is a very common stock tire size, I can't believe a tire shop around you didn't have them... weird...
225/45/17s are 25" in diameter, the 245/45/17s are 25.7" in diameter. So yeah you'll be sitting noticeably lower in the front from what it was.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.