Hi Mark, nice one for measuring up.
Since AE changed to steel from alloy for their axels, I am going to make a set up in either chromoly or stainless. Could do them ti but I reckon steel will be more than up to the job.
Durango have probably used 7000 or 6000 series aluminium up to T6 so imagine they are strong enough, let us know how they hold up Mark, when the spares get released