For the broken bolts. Unless you know someone with a mill don't let anyone drill it. It is easy to go off center. Then your screwed. The best way to remove broken bolts in cast iron is to build up the bolt with a tig weld,(not mig its brittle) Once you have metal protruding tig weld a nut on cool it with air instantly and turn it out. The nut and bolt? Take a sharp chisel and use the corner of the chisel to split one side of the nut. The nuts are soft and split easy. An air chisel would be the best. but a big hammer works. Don't try to easy-out those broken bolts , They broke for a reason . They are froze in the hole, so the only way is to drill and retap using a drill press our a mill to make sure you are on center. or do the weld proceedure. If you don't have these tools take it to someone who does.