At a bare minimum you need to rebed the lug. The "working face" of the lug will absolutely change from the old one.
The old stamped lugs are not the same thickness all the way around.
Therefore they'll project from the action at odd angles depending on thickness variations.
If the top (near the scope) of your old lug is .005" thinner than the bottom you can expect a .0025" discrepancy.
Your new machined lug should be precisely the same thickness. Usually they're deeper as well as wider.
You need to hog out the whole thing and start from scratch.

Personally I would rebed the entire action. Why upgrade the lug and cheat on the bedding?