This is probably a stupid question, but is it supposed to be screwed to the firewall just below the hatch, or should it be infront of the battery like the oters I've seen?

I "believe" the came attached to the front of the battery tray, but they were moved to the firewall when AC was installed. I've seen them both ways

AHHH, that makes sense, as this was a dealer AC car. (and a freaking hack job at that.)

I think I'll move it back (somewhere down the to do list, below get it running right)

You'll probably be missing the bracket, since they got thrown away, so just leave it on the firewall.