How Do You Mount Caliper On Front? Or Back?

i've installed disc brakes on a 1972 dodge dart. using parts from a 1975 dodge dart. mounted the caliper on back side, the brakes wont
bleed ,pedal goes to floor.the caliper bleeder is now about middle ways
should the caliper been mounted on front side ? and if so would this locate bleeder valve at top? any sugestions would be greatly appreciated