cody - welcome aboard ... your 86 FXR is going to have a significantly different strut bolt pattern, shape and width than the '90s - 10s' Dyna frames ...
... not sure what to advise as far as fender, but you might take a look at trying a fender from a similar year FLH or a reproduction from Custom Chrome, or Drag Specialties or V-Twin Mfg catalogs (if you're not familiar with them, try google) ...
... in my experience, about the best way to measure the width of your fender is to remove it and measure the distance between the struts ...
As the expression goes ... 'there's more than one way to skin a cat' ... I did a thread on my rear fender here ...
https://www.hdforums.com/forum/dyna-...r-for-fxd.html