A mod you might want to look into #39
Description
https://www.curseforge.com/minecraft/mc-mods/entity-model-json
It also has implementation for mods. I tried doing a pull request but couldn't get it to let me post.
I just found it yesterday, so I'm still messing with it a bit myself, that and I'm not as knowledgeable in how custom entity models works as I'm new to this - but thought I'd point it out to y'all.
If you could let me know if this makes the cut or not, I'd be grateful as I'm still getting into modding for personal use and would like to know if it's worth it or not to use this mod.