That will be very close to fitting without a spacer. It will depend on the tire size you use, and normal manufacturing variances. Tires of the same size from different brands will be slightly different. That's a given.
I've had 18's on my Mercury since 2007 that are 8.5" wide, and had to have 1/4" spacers. Counting the 6.35mm spacers, the offset is 29mm on these. I was using 265mm tires at first, and then moved to 255/55/18's later. I had plenty of space at the upper BJ, that's the critical clearance spot. If it's really tight there, you could smooth the edge of the BJ where a tire might touch, but I never needed to, I had plenty of room. I'd guess it was near 1/2" at standing position. I don't think a tire has ever touched.
So the 9" wide wheel will make it a test fit to be sure deal. I have used 17x9's to go on my 98 Limited soon. I've test fit the wheels, and hunted for years for an offset I could make work. I ended up with a 16mm offset wheel, which will give plenty of clearance, with 275mm tires. But that offset means I'll need a fender flare, which I got from a used 98 Sport(the thinnest OEM flare).
Fitting a different wheel takes some time and thought. I hope my examples will help you figure out what should work for your truck.