Detroit's don't need to be bled at the injectors like most other diesels (they are self-bleeding to an extent) but the fuel
supply system needs to be air free (check for sucking air leaks).
Most older set-ups have electrical
(or gravity) and mechanical fuel
pumps check to see if both are working.
In most set-ups fuel goes from tank to electric pump
to primary filter to mechanical pump to secondary filter to rear of head
(Left side IIRC), out front of head
to crossover tube to front of other head out back of that head through a restrictive fitting (to maintain pressure) back to tank.