Are these hub piloted rims or stud piloted rims?
If you don't know the answer to that question, then you better find out. If the are stud piloted, then go ahead... estimate the center and grind away. If they are hub piloted, I wouldn't trust anything less than a quality metal lathe for making the new center hole.
Is it a 1/2 ton truck? If so, then it's probably stud piloted. If it's a 3/4 ton or larger, then you better find out for sure!
