68 Cuda grill studs............ Any tips ?

Got the Cuda stripped this weekend , about ready to get it to the body shop , except when I tried to take the grills out , about 1/2 of the studs just turn freely in the grill.....
I soaked then in penetrating oil , cleaned what threads I could reach with a cordless drill and wire brush. Even held one with small vice grips while I used a wrench. It would only slip in he vice grips.
I could buzz them off to get the grill out , but is there a way to replace them once the grill is out .
Any tips , tricks , or advise guy ?????
Thanks
Donnie