Lower a arm spacer bolt size

[CJStefan]

Anyone know what size bolts replace the rivets on a '49 Custom? I'm putting Aerostar springs on and taking the shock out, I broke one of the lower shock plate bolts. Heat and vice grips were no good. Now the arms coming off so I can drill the broken piece in the drill press instead of crouched under the car. Figure I may as well get rid of the rivets while I have easy access to do it. That way if I decide to do spacers or need to remove the coil again down the road I'm one step ahead