My 1968 Camaro (80+k miles) had the same [single] hole elongation problem on the passenger side aft (rear) lower A-arm mounting -pivot subframe hole.
I fabricated a mild steel backing plate out of 3/16" thick stock. Oversized (L x W) and drilled to clear the bolt. The existing bolt has extra length to extend thru the added distance.
I prepared the frame, cleaned of paint, Mocked up the hole - bolt alignment and hired a moon lighting Nuclear qualified Naval civilian welder to (TIG) weld the plate in place using his remote portable gas powered TIG set up. We did this with the enginge in place and suspension in a state of disassy (No springs etc) We watched the heat levels and worked very carefully. Used tons of heat - slag - protection,,,kind of a firberous heat blanket as protection. (Refrecell (spelling?))
Painted black and no one is any the wiser for the reapair. Final assy and front end alignment accomplished and I am good to go.