205 will work just fine on a 7.5 inch wide rim. A lot of the 240 guys will run 205s on as wide as 9" wide rims. Some will even stretch them over 10" wide rims so your 7.5 will work just fine.
What's your offset? You might be fine running 215s. If you're going to run 205s, I would go with a 45 series because a 40 series will be very thin and will throw your speedometer off by quite a bit.