Diesel Bombers - complete turbo shaft separation

This is a TD04 turbo (10T) in my Dodge D50. Recently the old head gave up after a series of overheating events that undoubtedly did the damage to my turbo. It now has a much better head that comes from overseas models of the turbodiesel Monteros. I'm just trying to decipher what if anything can be done short of getting a new turbine wheel.

Basically instead of a turbine wheel with a shaft attached I have 2 wheels, the cold side impeller with it's own skinny portion of the shaft running through it. The turbine wheel is just free in the exhaust with all it's bindings to the shaft just disintegrated. And inside the shaft itself there is another rod which I assume was the original binding between the wheels inside the shaft. With the repair kit I can probably repair some of this but I don't know about rejoining the compressor wheel and the smaller portion of the shaft or how the 2 wheels connect together internally.

The wheels themselves are unharmed and the whole turbo is relatively new so I'm looking to get out of this without shelling out the $130 for a new turbine wheel. But alternatively taking it to a shop for balancing these wheels might run me more than that in my part of the country.

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OK i basically figure out what happened but still have no clue as to why. Basically the outer portion of the shaft just disintegrated is the best I can figure. It acts like it was starved of both oil and water which would have been basically impossible. So it seems once the turbine wheel is no longer part of the shaft the only solution is to buy a new 1. It would likely be possible to have another shaft pressed on but the cost would most likely be more than a new 1. I'd still like opinions on that though.