How to bypass 256 itemstack maximum for block entity?

I'm working on a block in 2023.2 with 2 GUIs. I managed to get this to work, but Minecraft's inventory capacity handling is capped at 256 and I need 554. After roughly 6 hours of getting the BlockEntity.java file to not crash I successfully loaded into Minecraft. However, the item "teleports" to different spots in the inventory if the slot number is above 256 and if there are other items in those slots competing for the same space the items from the 256+ slots are deleted. This seems to be an issue with overflow, so I'll need a new inventory management system, but I'm brand new to java coding and have only the experience required to get Bing AI to somehow spit out code that works (as well as a small improvement that allows me to not type         if (index == 276) return false; over 200 times, which is helpful). I have no understanding of code beyond the exact lines I worked on, and variables have no MCreator interface that I know of. Is there a way for me to make a new Inventory Handler? Also, I'm not changing versions. I don't want to deal with possible changes to the code when I'm already in way over my head.