Does a original 75 dart swinger with a 318 have EGR?
Yes, your '75 would originally have come equipped with EGR. Depending on the vehicle's equipment and build specification, it might also have come with an OSAC valve (described
here) and/or a catalytic converter. You will probably be happier without EGR, and it is unlikely you (in Great Falls) will ever face emission tests picky enough to flunk you for not having it on a '75 car. For a quick brushup on the various emission control devices and systems you may find on your '75, see
here.
Because you are new to the hobby, as quickly as you can, get and read the three books described in
this thread (which mentions slant-6 engines, but the books apply regardless of what kind of engine you have).