Sorry - I may have mis-read your post. I thought you meant the plastic/metal air guide inside the shroud was cracked. If you are referring to the alloy fan housing that is a different story.
I believe I have read/heard of people using JBWeld on these housings. The process was to drill a small hole at the end of the crack to prevent (or slow) crack propagation, then apply JBWeld to the crack. I can't comment on the advisability of this repair. When I discovered a crack in mine I threw it away and bought a different one. Check with Jerry at
www.euroeastparts.com for a used housing.
Still, however, if the crack is partial and has not opened up wide then it is unlikely to be the source of your rubbing. Patiently adjust the tightness of the nuts on the back of the alternator studs holding the assembly into the housing until you true it up. Again, start by making sure they are evenly tightened (use a torque wrench if you have one), then tighten or loosen nuts on the opposite side from the interference until it is squared up. It shouldn't take more than a quarter to half turn on a couple of nuts. Be patient; it will true up.
One more thing to check. At about seven o'clock the ground wire is fastened to the assembly. Make sure the ring connector is not between the alternator and the plastic air deflector or housing. This will affect the alignment of the fan as well. It should be the last thing on before the nut.