The injectors on the Perkins 4108 are not in the Perkins manual for the engine, well excepting an image showing one under test but nothing otherwise in the two manuals I have.
One manual shows an image on page 32?
Check the way the yoke sits high and under the neck of the main injector body.
I had my injectors fitted with new nozzles, they came back to me with the yoke reversed and a large gap where that joint is.
This meant that I could not tighten the injector into the head tight enough as the yoke was fouling the cylinder head and the copper washer was not sealing the injector to cylinder head correctly.
This is how the head was suppliied to me, the valves had been fully serviced, the injectors still required the same so the yokes were in the original and correct position.
I hope this information is of help to someone?