Calipers ? front or rear of center

i have put a couple disk brake swaps (junk yard style) and i always seem to have the calipers front of center on the front end . these were A and E bodies. My friend had a basket case 71 Roadrunner and asked me to pu it together also front of center he just picked up a similar 71 charger and it has calipers to the rear. Long and short Which is the CORRECT way for them to be