As a point of reference, I have M68 8.5" square setups with 255s and about 1-1.5" drop and no modifications to the fenders. The back is fine with no modifications and I run 12mm spacers in the front. I had 19" iForges on the car when I bought it. I think you're going to be fine with the 8.5/9.5 225/235 setup you mention.
However, keep in mind that 10mm is equal to about 0.4 inches. So if your rear wheels are 1" wider than the front but your rear tires are only 0.4" wider than the front, things may look a bit off. You might want to consider running 225/245... IE: keep the 20mm front to rear size differential.
Anthony Colin Bruce Chapman: Adding power makes you faster on the straights. Subtracting weight makes you faster everywhere.