The 3D Player Model is located in resource/ui/HudPlayerClass.res
We can find the code to add a player model HERE Copy the code and add it at the end of the HudPlayerClass file and the playermodel should now show up if it isn't check if cl_hud_playerclass_use_playermodel is set "1"
If we want to edit it we need to work with the various angles, origin, frame, fov values. Is possible to rotate it vertically, horizontally, make it bigger etc… just experiment with the values a bit!