Plumbers solder which is what appears to be used here and electrical solder used to contain lead, today leaded electrical solder is mainly used by small businesses and hobbyists in part due to the difficulties of making good joints/connections with lead free solder, large companies can afford the automated equipment to do the job without damaging components at the higher temperatures required. I don't know whether plumbers solder still contains lead.
Some years ago I read that some museums will no longer accept ship models with any lead castings/fittings as over time the lead oxidises to a white powder. Perhaps a consideration depending on how long you want your project to last although as museums think of preservation in hundreds of years, maybe not.
I love the potential of this but before I'd go ahead I'd make sure I had plenty of ventilation for the pour, I'll also be wearing a mask & looking for some way to catch the solder dust off that sander before it settles on everything in the shop.