You need to get those studs out of there with a vice-grips like a user said, Have the car jacked up in the front with tall jack stands, then tilt the whole header downward at the collector. The starter will slide out once turned the right direction. If you HAVE TO, put on the nut still flush with the troubled studs, then hit it with a mig welder and weld the nut to the stud, to get it out.