Shashi, If the problem stems from being an aftermarket part, IMHO a part that far out of spec should not be used. Can't be sure the metallurgy is correct or the taper is right. People do odd things in an attempt to make repairs like ream the knuckle taper. Do you have the old ball joint to compare the new one with?
Is this problem only on one side or both sides? If you can determine the taper is correct and is fully seated top to bottom then you can probably get away with a spacer. Tapers are very specific. Ask any knowledgeable machinist.
Where did the new ball joint come from? If not from a reputable vendor, I suggest buying a new one from reliable vendor to compare.
Personally, I would not leave it that way without further investigation.