niel_petersen said:
I suggest clamping the stud in some soft jaws in a vise & seeing if you can get the nuts loose from those studs that came out. Then double nut them & reinstall the studs using locktite & screwing them in as far as you can.
Then when you are assembling the exhaust connections, use some hi-temp anti seize on all nut threads so the next time things will separate at the nut/stud interface.
Better yet of course is to install a new stud. But either way, use antiseize!
Yup, I was gonna suggest anti-seize too.
I'd put the stud in a vise or grab it with a ViseGrip. I'd heat the nut or at least let it sit with penetrating fluid over night. If heat is used, heat it first, then quench it with cold water, then apply removing torque; this is less likely to damage the threads when removing the nut.
If the vise or ViseGrips mildly gall the threads of the stud, that's not bad, it'll help the stud stay in the block. Agree with the suggestion of red Loctite on the engine block end of the studs and anti-seize on the nut end.
HTH