If this is the four valves per cylinder engine, the valves set at .026 on the outer part of the bridge, this gives .013 on both valves. The valves et when the injector arm pushes down on the injector. The injector sets with a timing pin, should 1.460in. and sets when the valve rockers go down, opening the valves. Detroits have tendency to suck air it the filter housing or at fuel lines. To check, take the line going to the fuel transfer pump and make up a test line into the fuel tank filler or another fuel container. This will eliminate the fuel sudtion system. Everything after the pump is under pressure and would show as a leak. One other thing to check would be to put test gage in the secondary filter, the one after the pump and be sure the pump is putting out 60psi at full throttle. Let me know what kind of information you need, I think I can help.
5043-7001 is a 4-53. You are correct in thinking that. 4-71 would start with 1047-7001 or such . The 4-53 has bolts around the edge of rocker cover to hold it on, the 4-71 has two bolts or knobs in the center of rocker cover. that hold on the cover. Fuel systems are very similar and the 53 series is a higher rpm engine than the 71 series.
thanks curtis, it was sucking air ,changed out the lines and resealed the fittings and it ran like a champ.