Bear in mind the stock axle washer has a rounded lower surface to match the curved inset on the mating halfshaft hub. Putting the washer in upside down will soak up part of the axle nut torque by bending things without contributing to assembly tightness. The shop manual torque is too low. No need for tricky nuts- the desired torque on that axle spanner-nut is 350-400 ft-lbs. Properly torqued, they survived LeMans & other contests just fine. Do not worry about stripping the threads- the SAE says that a 1-1/2" fine thread like this in mild steel strips at around 1200 ft-lbs! And please- do NOT use red Lock-tite. Poor guys like me have had to remove such nuts with a cutting torch after breaking a factory socket.
Leaving the axle nut washer off effectively lengthens the axle so the splined hub may bottom on the axle splines before things ever contact each other. So the parts will normally be sloppy-loose even at full torque. Both Wilkinson & Larry at PanteraParts.com in NV have new repro nuts & washers in stock, cheap. Good luck.