To be honest I was not expecting anyone to jump onto this so quickly 
This is my first serious attempt at a mod and I was unable to find any up to date documentation so I sorta jumped in and started trying stuff, and those body types you’re seeing are:
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Not set up correctly, I was just tinkering to see how hard it would be to add body types and as you can see I can add them pretty easily, but because I didn’t have sprites I actually stripped out the code for those body types since I ended up just using the 3 basic body size sprites instead.
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I’m making the mod first, tweaking things second, so right now any and all compatibility with other mods is purely coincidental. I tried using character editor with my body types and had similar problems, but that’s a problem for the future.
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I think that headless pawn bug is because the pawn has clothes on. From what I’ve tested, it seems that when a pawn is rendered, the game uses the names of the image files to determine which images to use, specifically the images are named in a [label]_ [bodytype]_[direction] format. All the body type images say Naked at the start (ex. Naked_ChubbyFemale_north.png), and all the clothes say the name of the clothing and then the body type they are for (ex. Duster_Thin_east.png). I noticed that if a pawn has clothes on and there is no image file matching the body type of the pawn, the pawn generates naked and headless, and sometimes they’re even completely invisible.