The Machines add-on to Simple Ores, which I maintain, features what appear to be modded furnaces, blast furnaces, and smokers. They are not actual children of the corresponding vanilla classes; they are custom machines that process smelting, blasting and smoking recipes. Apparently, Polymorph does not work with them.

It was pointed out by one of my beta testers that Mythril Blast Furnaces and Onyx Blast Furnaces "don't interface with Polymorph". I think it would be very helpful for modpacks if they did. So, how do I help integrate Polymorph with my machines?

Main source code is here: https://github.com/Sinhika/Machines

Supporting library is here: https://github.com/Sinhika/SimpleCoreLib