Installing SS springs

I'm doing the SS swap on my Demon soon as well. I bought all new rear spring shackle bushings for the job but am wondering what the bolt diameters are so I can pick 4 new bolts up prior to installation day. The I.D. of the new bushings is 1/2" but the bolts on the car appear to be smaller than that, say 5/16s or so. I'm guessing there's a metal spacer that slides inside of the rubber bushings? Can I reuse that? Could I just upsize to a 1/2" bolt by drilling out the shackles? Any info is appreciated!