I'm getting ready to order new axles from Moser. Here is what I measured using a digital caliper & tape measure. Dimensions taken with a tape measure were after I leveled the axle on my bench and then used another level to measure to off the end of the axle. I measured the axles twice on two different days and came up with the same results.
Here are the stock Mustang II measurements with 4 lug 4-1/4" pattern: 
Here are the stock Mustang II measurements with 5 lug 4-1/2" pattern: 
Hope that helps someone.