front subframe is the front. it bolts in at the firewall and under the floor. it is one piece. the rest is unibody with rear framerails welded in.
it will be a bit more than quarters and floors, but if you can handle them, you should be able to handle this, i think.
maybe cut all that crap out and just tub it? buy one of those rear frame diff sections?
front sub is no problem,. there are repair patches, and other models will fit if it is bent. also there are new replacements with better geometry and lighter frames if you have the $$$.