GV, The ideal & fastest method is a torch & a good air chisel, warm up head & chop. Since thats not really an option for you. The grinder will work, but your going to eat allot of grit & sparks. A GOOD air chisel will probably be easier & allot less sparks. Knock the heads off & use a pointed chisel to push out the center. Use grade 5 bolts & nuts when reinstalling the parts. Cut the bolts an 1/8" from the nut & peen over the threads so the nuts wont back off. Lorne