What material to use for geared shaft

[Pete O]

I removed and dismantled the worm drive gearbox this afternoon. I think the shaft is actually bent inside the worm gear, as the outer end of the shaft is unsupported it wouldn't take much to bend it, perhaps lowering the knee with something uner it or something like that, then the gear has been forced over the bent section of shaft by screwing the Y feed in. Here's the contents of the gearbox:
   
It all seems to be undamaged, except for where the shaft has been cut at each end. Here's the worm gear with the shaft jammed inside it:
   
I heated the gear gently with a propane torch to see if I could get the shaft out, I can get it to move maybe 3/16" either way but that's it, don't want to force it and damage the gear. I have a plan for getting it out, would appreciate some feedback on whether this approach is likely to bear fruit; if I chuck it in the 4-jaw with some soft jaws gripping the large diameter of the worm gear, face the damage shaft and then centre-drill it, drill it out to almost the full depth of the gear, making a blind hole, gradually increasing drill size until I cut through into the keyway, then use a punch to drive it out. With the shaft drilled out to the keyway, it should be able to collapse as it is driven out, hopefully not damaging the bore of the worm gear.

The gearbox casing is a concern, I think it is beyond welding:
   
   
Someone has already had a go at it:
   

I'm open to opinions, but I reckon this is not going to be repairable. It is cracked through both bores.
Thinking about casting a replacement, is there any reason why I could not do it in aluminium?