since most of the .48 turbine housings are cracked, is there anything you can do to fix it? I'v heard many people say its cast iron or cast steel. Is there any way to tell?

Also, is it possible to just grab any turbine wheel and swap it in place of your existing one? or is there something else too it?

 

UltimX :Yes, unfortunately changing the turbine wheel involves a complete preventive rebuild of the turbocharger. By changing the shaft, bearings may need replacement and rebalancing of the rotatin assy is absolutely necessary.

Yes, I can fix the cracked turbine housings. extensive excavation of the crack is involved prior to welding and heat treating of the welded part is needed to prevent cracking and after that some machining and custom porting is necessary.
Actually, thermal stress is the reason why they crack in the first place:
It's the case with all cast parts with uneven mass distribution such as the ford style turbines which obviously have a very bulky heat absorbing side and the other side full of holes with sharp edges and yes, they all crack right in the middle of the wastegate dump hole after X hours of thermo-cycling. It's important to remember that fixing such cracked turbine doesn't cure the initial design sloppyness of the part and it may very well crack again eventually, especially if used in a peformance application at twice the heat it was designed for.