One thing that people don't think about with ventilation is the need for fresh air to come in to the area in order for stale air to go out. If you can bring some makeup air into the room across from where the air is being exhausted that way your exhaust fan will be running at max and not creating a vacuum in the room.
You don't want the fumes just blowing back in the room, so put the exhaust down from the prevailing wind, or try to seal off the exhaust as well as possible. And yes, balance the airflow by having a fan bringing in fresh air, preferably as far away as possible from the exhaust! And a "mask" should be a respirator that has cartridges rated for lead fumes, not just a dust mask. A good leather apron would be adviseable as well. 3rd degree burns are never fun. I've done babbit bearings before and it can be some evil sh!t.