Hello Buck,
I looked back through my photos, and unfortunately, I didn't take any of the underside of the Orchard fender extensions, or of the slot cut into the standard Pacemaker fender. I did take some photos of my "dry fit" of the reproduction fenders before I painted them, have taken some photos of it now to point out a couple of things.
There is a "pin" in the fender extension that fits into a slot you need to make in the normal Pacemaker fender. I have drawn an arrow pointing to the location of that pin. The reason there is a slot for the pin is so that you can put the pin in the slot, and then roll the fender up to slide it under the front hold down bracket (arrow on the photo with the unpainted fender flare).
On the back of the fender extensions, there is a long rod threaded on each end to secure the back of the fender to the brace on the bottom of the standard fender. I also took a photo of that.
This might not be much help, but take a look, and let me know if there are any other specific photos I might take to help.
Regards,
JB