Does any one know if a brake caliper off an 82-84 wagon or hatch will fit the front of a 1978 4wd wagon LT

yes it will. Actually if you want, the whole vented brake assembly minus hub will bolt right onto the hub of the '78. This is the same setup as my '79 4wd wagon I have BUT I also used the EA81 control arms and hubs. I had to make a custom stabilizer bar for it but that wasn't too hard since I made it exactly like the EA71 stabilizer bars, same length but different thread pitch at the end. If you need help or have more questions, just PM me about it and I can help you step through it. If you do go with the vented rotors, it'll be a lot easier to get parts for them, might be a little cheaper AND, you'll have more braking power as well.