If the original headset fit and worked properly, it's reasonable to assume the frame and fork were properly prepared. Machining it anew can't make right righter, but there is the potential to screw it up.
Best practice is to follow rule number one -- "don't fix what isn't broke.
As long as the new headset is the same standard as the original, ie ISO vs. JIS, it's a straightforward, pop out and replace.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.