Got this Zilla an peg holes were stripped out plus needed to put a skid plate on it so I used a smaller diameter higher grade longer bolts for the shifter side an front bolt on right side I also used serviceable lock tite an lock washers on all bolts. u cld also use those nuts that have plastic on outer end to keep nuts from loosening up or falling off completely. the longer bolts allow u to go rite thru frame. an delete inner peg bolt threads completely. an just remember the back right side peg hole doesn't have a thru hole in it like the left side does. Another option for that is to use a threaded insert just find the proper size an go from there. An as a last resort u cld jst drill a thru hole in it but remember it will weaken the frame. Cause there must be a reason Suzuki didn't drill a hole thru the frame in that peg hole.
I replaced a set of stripped & wollered out peg mounts on a customers zilla with some new ones I machined out on my small lathe. IIRC, I used either a 5/8" or 3/4" metal cutting hole saw to remove the old ones then welded the new ones in place.
I think you can also drill and tap the stripped hole to the next bigger size as well.