Kind of Bolts for my truck Seat?

I bought a set of used seats to replace my bench seat in my Int'l 4700. With it raining here, I'm thinking tomorrow might be a good day to make the retrofit. I know it sounds like an easy application, but I don't want to screw up and find myself straddling my steering wheel while trying to avoid maw maw. What grade screws/bolts should I use to bolt my seats to the floor? The holes in the brackets look like they're 3/8". Not looking forward to drilling through the floor of my truck.