Random images from the web. Left-hand axle on the left with the upper nipple (albeit angled instead of straight) facing forwards and lower facing backwards. Right-hand axle has both facing forwards, with the correct short nipple at the top (where a bulge in the casting brings it forward) and a longer nipple in the lower position:

Rather than the two straight nipples being the same length as indicated in the top picture, the upper one is shorter as it screws into a bulge in the casting which gives clearance for the grease gun. The lower has no bulge so needs a longer nipple. Also shown is the two-part assembly of some angled nipples, although it appears that some might have the straight part pressed into the angled part rather than being screwed:

I have compared these and other angled ones and short of a microscope cannot see any difference in the thread shape, not even in the pitch. However most only have three threads exposed which makes that difficult, and indicates that for all practical purposes they are interchangeable, even if they do have different threads!

Between the upper and lower king-pin bushes there are two 'dust excluder' tubes - and upper (12) 1G4271 and a lower (9) 21B251, a spring (10) 2K8951, and two seals (11) 1G4217. The tubes and spring are available as a kit from some suppliers: (Leyland Parts Catalogue)