Below is a picture of the comparison of a STOCK Ford speaker cutout as most all Mustangs/Capris would have come from Ford (top) to the panel that was originally in my car and has an obviously far smaller hole. Therefore Ford must have delivered my car to asc with NO rear cutouts. Whether this was requested by asc or not or just Ford's interpretation of the build...who knows?
Below is the first set of Kenwoods I bought ($20). Note the tweeter sticks out. The asc Kenwood cover would not fit.
So I got another set of FLUSH MOUNTED speakers (1668S). These if skewed to 45 degrees would accept the speakers covers. There are bumps on the speaker edge which the cover grabs. I was amazed to see two parts separated by 20 years work like they were made for each other.
Finally, here is the installed item. Two holes in the speakers had to be drilled so that the speakers could be mounted to the stock holes and have the "bumps" in the right orientation for the speaker covers. Then in a vice with the screws in the holes, I had to tap them and push them down so they were flush. If I didn't, the head of the screw was interfering with the speaker cover pressing onto the speaker completely.