Putting this here for future reference:
The methods I’d read about before used a resin printer – mucho more expensive compared to using PLA on a filament printer.
More notes. What you need is Alloy 655 bronze – for example, this, from Online Metals.
Bronze melts at around 1,742°F (950°C). Here’s a foundry for short money, the Nelyrho 6kg Stainless Steel Propane Melting Furnace Kit Temps get up to about 2552°F (1400°C).
Got a new roll of Overture PLA and fired up the old printer – here’s our test cleat: