Mid to late '80s atv fast machines were basically the first of their kind.
If you want to have nerf bars, you can probably make a set for another Yamaha, with built in heel guards, fit. The '87-88 machines are kind of unique with out much aftermarket parts for certain things. I made a carb model YFZ450 nerf bar set fit fairly easy on my '07(but with factory heel guards).
A welder can overcome anything with enough beer and time. You might be able to just add frame brackets and be set.
I got my leg under the rear tire of my past '87 Warrior once. I get why you want it. Maybe some u-bolt clamps could be used to attach them to the frame?