As far as the GFCI code doesn't specify the location. There used to be an exception for outlets over 6.5' but I think that is gone now. I would add a new wire so you don't have the safety concern. If the walls are closed you may have to fish the wires through the walls because the old wires should be stapled to the studs and pulling the new wire with the old won't work with the staples holding them in place.
It could be worse
Copper thieves could have taken a bunch of wires, leaving you no idea how things were ever hooked up.
So you have to get your multimeter and start testing stuff, and some of this must be done hot. Figure out which wires are your power supply. Figure out which breaker it is on. Bonus points if you slap a GFCI breaker there to keep you honest. Make sure it doesn't trip before you start.
Then you have to move through each group of wires and figure out what they do. I wouldn't throw power on any lines until I have made sure they are not a switch, by checking for resistance with switch(es) in all positions.
Hook up the grounds first, in any case.
Having a few incandescent bulbs and dollar store night lights helps a lot.
One of my most useful tools for that is an appliance cord and two wire nuts. If you have a pair that reads infinity ohms until you plug in a nightlight or install a lamp bulb, splice their hot and neutral into the cord, plug in to a supply (fed off another circuit of course) and see what else lights up.
Work through it, labeling or diagraming as you go.
It really helps if you know how to do electrical wiring. If you don't, you won't know what you're looking at. For instance, that 3-wire bundle black/white/red probably has something else going on.
Best Answer
Assuming that one cable is the incoming power and one goes out to more outlets or lights, just keep everything connected by color--blacks together and whites together.
I'm a little concerned that you're doing electrical work without the skills to trace a simple circuit, though. Please be sure that you have an understanding of proper connection techniques, wire size requirements, and other best practices. A little reading of a house wiring guide would be wise. You don't want to burn your house down.