You'll need to cut the broken stud off flush with the manifold and then drill it out and retap the threads in the manifold. The bolt size is 5/16 coarse thread I'm pretty sure.

The mounting clamps are easy to find at a junk yard. But if you can't seem to locate one, then let me know and I'll send you one.

If at first you don't succeed,
then read the directions and try again.