When I was swapping the 35 mm front end onto my 75, I wanted to use a later style fender. The 75 without the braces looked kinda poorly with the holes.
I bought an XS1100 fender, looked the same in the pics. Put it on, looked very nice till I rode it.
The brace under the fender acts to stiffen the fork as well as support the fender. The 75 fender has a much heavier brace than the XS1100 fender. The XS1100 has 37 mm tubes and as such are very stiff. they don't need the heavy brace.
Try to get an XS650 fender, you need the heavy brace.
Leo