Yep......trying to get them right for a paying customer was a pain.
for screw in one's at the chainstay we used a variety of spacers to try and get them right. If there was a clip then that was "it" unless you drilled out the clip and used a bolt. have you got a pic from underneath to look at the chainstay bridge. ?
I remember fitting a set of alloy guards for a customer who then had a fit because he thought he had bought blue metallic......that was the blue film they used to protect them. Places like Woolies who sold bikes never took the film off the small sport mudguards. I used to pick the film off whenever I saw a bike parked up. Wonder what they thought when they returned to their bikes and they had silver tiny mudguards and not blue