I would think that if both axles have lockers then the stress would be distributed between the 2 (front and rear)
I'm guessing the same. Therefore chance of rear-end breakage would presumably be reduced, right? But that's one study that will never get National Science Foundation funding
I figure with two auto-lockers, then the four banger powering the entire front/rear locked drive-train at the same time isn't going to be the same power to the ground per wheel vs when powering just a locked rear end.
Even if momentum leaves you with just one tire on the ground in the rear and the front tires both in the air, you'll still not be putting the same torque to that one back tire with traction as you would with just the rear-end locked.
But I guess the rear-end 35 breakage is more of a no-traction, then sudden-traction thing. And even with the 4banger driving both axles due to two lockers, you might not be talking a significantly reduced torque burden on a locked rear end paired with a locked front-end (unweighted or not). Maybe 5-10-15% if you are lucky.
I'd still probably go with a rear-end swap just to be on the safe side if you are locking the rear.