If the hinges holes are egged out,they can be welded up and re-drilled--or you can do what I've done with ones I did for customers who wanted a cheapie fix,I used a "step bit" drill to enlarge and true up the ovaled holes,and used long grade 8 or allen head 7/16" bolts with nylock nuts instead of the original pins,after drilling the hinges out to 7/16"...
I've also used some thick 3/8" washers ,or old rocker aem balls as bushings,I welded them over the ovaled holes and used longer bolts instead of the hinge pins..
Easiest fix is to just buy new hinges from GM,but they are not exactly cheep,,