Without taking too much of your time, can you explain what about it makes it a C# mod? Like, what part of the functionality requires C#? Cause if it's the automate integration I could totally live without that. I just want a furnace that uses the old sprites and has the seasonal skins. Is that doable with just CP? I have a mod for the bus that does seasonal skins (though I have no clue if it uses C# or not. Are those the ones that have the .dll files that you can't open without downloading a special program?
You're not taking too much of my time! I love helping.
TL;DR - Yes, based on the furnace mod I linked (as a potential alternative), it should be possible to make Industrial Furnace into a CP mod.
I'll answer your question(s) below:
What makes it a C# mod is the fact that Industrial Furnace, as it is, uses a DLL. A DLL is a dynamic-link library that allows SDV to inject new functionality directly into its memory and use it. This was, and kind of still is, the best way to make sure a mod does exactly what you think it does. Post-1.6, this mod can probably be turned into a CP mod (as the other mod that I linked that started this discussion is a CP mod).
How can you tell if something is a C# mod or isn't? If it contains a DLL and if the manifest has an "EntryPoint" entry in it. CP mods will typically have "[CP]" or "(CP)" somewhere in their name (usually in the beginning) and have a folder set up that must contain a content.json and manifest.json. For this particular mod, you'd probably want an assets folder that holds the actual images/sprites for the mod that get referenced from the content.json file.
If I took some time to study the other furnace mod and could get the images from the mod in question, I could probably create a CP version of it. But I'm not 100% sure how well the other furnace mod works and there are some fields that the furnace "building" needs that I'm not sure if it needs them or not.
Hope that helps!