Worked in polishing and plating, did mostly prep. One thing I remember, plating required absolute cleanly ness, as in no Oxidation, and no grease or compounds.
I remember nice plating jobs being ruined by 1 spot of oil, or oxidation.
We would dip Items in a hot formaldehyde bath to strip all oils off them. Or collar buff them with talced gloves on, then handle them with gloves untill they got plated. One thing I also remember is that if parts got oxedized at all they had to be repreped.
I have never been involved with lead plating but from other experience my suggestion would be to get them to cast to the right size then go straight from casting to the plating tank asap.