To prevent the lead flash/seepage you can do what I do when I modify a mold for hooks.
Fill the cavity with red RTV, do this on both sides of the mold. Apply a liberal coating of talc powder (baby powder). Now place the form in the cavity and apply some more talc. Close the mold and clamp it closed. Wait 24 hours, remove the form, blow out the talc and start pouring.
I've had to do this with some molds to prevent the lead from flashing around the hook eye. On my smaller banana head jig mold if I use the EC 635 black nickle hooks the lead will flash. A small bit of RTV saves me a lot of time.