I'm working on making a skull item for an entity that i made. I want it to be wearable similar to normal skulls in minecraft, place-able on armor stands, and when you place it on a block, I want it to chose one of 2 models that I have made based on whether its placed on the top of a block or the side of a block (what normal mc skull blocks do). I'm about 5 months experienced with java but I just started modding Minecraft a week ago. To me, since the block basically has identical properties to normal skulls but just a different model and texture, it seems like there might be a shortcut to essentially copying the vanilla skull code or editing the vanilla skull code to include my skull. Would anyone be able to answer what the most efficient way to accomplish this task is?

Definitely looking at vanilla skull item and try to replicate its behaviour in your custom item is the way to go here. Editing the vanilla skull code is not an option in this case