How do I make an item place a block with its rotation based on which half of a face of a block the player is looking at?

I'm currently making a mod which has slabs, vertical slabs, stairs and what I call "corner posts" (8x16x8 blocks with its model aligned to a corner of the 16x16x16 pixel area it occupies) made with Concrete and all of its coloured variants, and I want the placement of those "corner posts" to mimic vanilla slab placement, but its flipped horizontally and also works on corners of blocks. I would LOVE for the "Look [cardinal direction] position of [event/target entity] with raytrace distance [number]" procedure blocks to have an option for using floating point numbers instead of integers, but for now, I need help. Here's the model in question:

Now, before you say "HaVe YoU tRiEd ThE "[cardinal direction] value of look angle vector of [event/target entity]" pRoCeDuRe BlOcK???", I did. And it passes straight through blocks.