Get a long piece of threaded rod and some matching nuts. When you press the races into the frame you never want to push on the bearing surfaces or the inner race of a cartridge bearing. Use either large diameter washers that contact the outside of the cups, or on the inside if the cups have an inner ledge. A slight chamfer on the inside of the frame, and some grease, will help get things going. Oh, and yes, remove the paint on the top and bottom of the head tube where the cups will seat. Of course, having the head tube faced first is best if the builder did not do it already.