On my Wart Hog bike,
it has an tapered head shank for the the steering/handle bar,
shank part of the front fork, 1-1/4" top to 1-1/2" bottom end.
I used a 1-1/2" star nut and inserted it into the bottom of the taper,
to get a secure hold.
Then I made 2 mild steel plates with a center hole, one plate to fit inside the fender and the other to fit on top, then used the correct size/length of bolt to go thru the steel plates and fender, when tighten up, it holds the fender very tight and it does not move.
You can see the red colored steel plate on top of the fender in the photo.
Here is where I got the star nut from :
I added a couple of tubing clamps used for off road light bars on the front fork columns to give a place to attach the fenders stays, note that my front fork slides/moves from the bottom end.
Use these types of clamps with an adjustments spots that you can adjust to fit the distance/spacing for the front fender you need.
The front and back fender kit has enough fender stays to do the rear and front fenders, I got this extra front fender to use on the front as I wanted better coverage for the batteries/motor for all the clay mud I have around here.
There is a place across the pond (England) that has a good selection of wide/full length fenders, but they were always out of stock for the ones I wanted.
When searching, do not get the Ping Pong paddle type of fenders, they are a joke and don't provide the coverage I needed.
Look for 4" wide =100 mm+ by what ever sized tires you run.
I hope this helps, if you need more info, please feel free to ask me.
Tia,
Don