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The JHeretic resource pack includes everything for Heretic; models, hi-res textures, hi-res hud etc etc.
If you literally want everything except the models, you can just turn models off in the control panel.
If you want to disable other components though...
Doomsday's Snowberry launcher has the ability to allow the user to select components of an add-on, if the add-on is set up for it (see the JDRP for Doom). However, the JHRP was not set up for this.
If you want specific parts of it, you have to open the JHRP pk3 and extract them, which is very easy to do as a pk3 is just a zip with a different name.
For instance, the 'GUI-jHUI_gui.pk3' inside the JHRP pk3 contains all the gui stuff (JHUI). You can extract this pk3 and run it by it'self.