I don't know what the sleeves are made of, but a pneumatic chisel makes very short work of them.
I am not theorizing here, I have done it several times.
An NA housing can easily be drilled for the water passage to the turbo.
Really, turbo housings are the same as NA housings, with a little additional machine work (drill hole out, remove diffuser)
I had trouble with the roll pins, but I didn't try the MIG and vise-grip idea.
edit: there is no difference in the sleeve (except for the diffuser) and the NA sleeves flow just fine (once the difuser has been removed).
The turbo port timing is identical to the NA.
The REW port opens earlier, hurting fuel economy, raising EGT and mildly improving flow.
Here are some pictures:
NA Sleeve
NA Sleeve.JPG
NA Sleeve w/o diffuser
NA-diffuser, looking in.JPG
Turbo Sleeve
Turbo sleeve.JPG
Streetported turbo sleeve
streetported turbo.JPG
RE/REW ?? on left, NA on Right
REW next to NA.JPG