Natural structure generation using blocks

So I am currently working on a few different large structures for my mod, but when they would generate in normally they would often be cut off on one or two sides. After some research I learned that this is due to chunks not loading these other parts of the structures, and that the solution is to instead use blocks that generate the structure through procedures. On trying this, however, I have not been able to get these blocks to generate the structure naturally, and it only works when I hand place the block. How do I get the structure to spawn through this block without having to place it by hand? Any help would be greatly appreciated. Attached are some pictures.