furnace requiring 2 fuel slots

Sorry, I know there are a lot of questions about ovens, even with the same question, but I couldn't find the answer. Basically what I am looking for is to be able to make a furnace with 4 slots, one for the object you want to burn, another for the outlet and another to put the fuel, what I am looking for is that the furnace needs 2 sources of fuel.

In my case, it's not exactly an oven that I want to make, but it does the same job.

This is what I did using Pylo tutorial https://www.youtube.com/watch?v=asuMnQNgKKE&t=418s

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and this is what I want to do. I have tried various ways but could not, when I click on the "furnace" the game crashes.

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These are the procedures I use, which are what Pylo uses in its tutorial.

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If anyone wants to directly interact with the mod, here is a link to the workspace: https://www.mediafire.com/file/pc1bveykof23ti3/potted_crops.zip/file.

And if anyone wants to contact me, I'll leave my discord here: ZacKDA # 1434

important (i think): i am using mcreator 2020.2 version and the mod is for minecraft 1.12.2 as this is for a server on that version.