Front differential housing cracked?

Would you please upload a picture of the axle and the crack. The answer would depend on if it's cracked and which axle it is.

Ouch, that isn't a common thing with those. With where that is broken, and it looks like an old break, I would suggest replacing the complete front differential. There are bearings and bushings in there (circled parts) that will be damaged and metal from those pieces will be in the lube. Replacing the complete unit would get you all of those parts in one shot and also take the truck out of service for far less time. You will need to look at the mounting as well because that unit is mounted using rubber mounts that don't move that far. As for replacing, you basically unbolt the outer axle flanges from the front inner CV joints, then the driveshaft. Disconnect the electronics and unbolt the unit and take it out, reverse the process to install the replacement. Verify the axle ratio and any options then hunt up a replacement. Car-Part. Com might help with that.

Not the same part. There are a few versions of that front axle, you need one that matches the part you took off.