The safest and usually best advice is to run fuel injection components that were made/calibrated for a particular application. i.e. Use 6.2 injectors with 6.2 pumps and 6.5 injectors with 6.5 pumps. Now... these injectors are calibrated to "pop" pressure using shims. If you had the right test equipment you could recalibrate 6.5 injectors to 6.2 specs.

Using 6.5 injectors with a 6.2 pump could cause hard starting, especially while hot (the pump might not be able to generate the pop pressure at cranking speed with hot thin fuel). And, a delayed pop could possibly retard injection timing enough to be noticeable. Jim