I had a similar problem with my leaf springs. I was able to open up the holes using a very good HSS drill bit (Walters), lots of cutting oil and slow speed. Instead of the standard spring bolt, I used a 3/8” hex socket head capscrew. These are a lot tougher than the standard spring bolt and the head fits nicely in the spring perch without having to drill it out. I used a longer than required capscrew so the smooth shank portion rests inside the holes of the leaves. Then just cut off the excess.

Garth