72 Duster build - Pro touring slant six

Do you think another 3mm of positive offset (1/8” more backspacing) would have been enough to avoid rolling the fender lip? And was the trimming at the corners on the top of the fender or at the bottom corner?

Nope. It needs more than an 1/8" to clear with a 9" wheel unless you run an extreme amount of negative camber or raise it up. Also if you pushed it in it will just rub worse on the other side. With my 9" wheel it just barely touches the inside at full lock so another 1/8" will make it much worse. With an 8" wheel (depending on backspacing) I think you can get away without rolling the lips but anything over a 245 series tire requires modifications.

For the trimming I had to cut out a good chunk at the bottom corners on each side. The rear didn't take much (I cut a little too much) but the front needed to be cut almost flush to the support rod. I had this photo on my phone but I can get a better shot later. I also had to change the splash shield bolt for a little extra clearance.

wheel cut 1001.jpg