As you know, if you dovetail it, you will need to redrill it. If the hole is already near the edge, it may be too short after dovetailing. Or the drill may want to wander into the existing hole, and go off center. I would probably procure a new one and start fresh. You may need to recut the lug channel slightly one way or the other to seat the new lug. Also, I would drill from both sides toward the middle to avoid run out of your existing pin holes in the forearm. Not hard. Just takes a little extra attention to perform a neat job on the replacement.