It takes a customer with a VERY deep pocket to make me do any lead work these days- - - -I make it expensive enough to be painful if somebody just has to have that kind of work done!
About 30-something years ago we started using a resin-based Ditzler product called "Aluma-Lead" in places where a metallic filler was needed, such as for rebuilding rusted-out window channels, etc. It was atomized aluminum powder mixed with a fiberglass resin liquid carrier. It was necessary to sandblast the area first, do a thorough cleanup, and then apply the filler over a cardboard backing. When it cured, it could be filed, sanded, and painted like aluminum. That product was dropped from inventory when PPG bought out Ditzler several years ago. Now if I want a metallic filler, I use Devcon Epoxy Aluminum or Epoxy Steel. Lead only gets used on a concours restoration job, and if you have to ask what it costs, you can't afford it!
Jerry