The short answer. Probably not.
The long answer.
Fitment of the 8" wide rim will also depend on backspacing, not just width.
With the posted rim of 17x8 +40 you will have a 6.1" backspace. In order for your stock rim to have that same amount of backspace on a 17x7, it would need to be a +53 offset. This is not likely with a stock rim since they tend to be in the 0-20 range.
A quick and dirty way to find out what your backspacing is, is to lay a straight edge across the back of the rim (on the lip, not the tire). Then measure straight down to the back face of the rim where it seats against the car. This will be the backspace. Accuracy is questionable depending on how good you are, but it will get you in the right ballpark if you can't find the stamps.
To get an accurate measurement of the width, and diameter you need to remove the tire, so I'd recommend finding the stamps.
Another thing to consider is that you'll likely need a new set of tires too. I know you said the stock tires are good and you want to keep them, but if they are the stock Goodyear Integrity 215/65/17 tires, they are too small for the rim. The approved rim width by Goodyear for that tire is 6.0-7.5". An 8" rim will be wider than what Goodyear designed the tire for, and some shops won't install them as a result. However some shops won't care as long as they can get the tire to seal on the rim. If you find one that will install them you have to keep in mind that the maximum speed, cornering capabilities and load capacity will be reduced.
So that's the long answer. Not the news you want to hear, but I don't think those rims are going to work for you.
