gamma crux is a M3.5III red giant star. The TiO bands are more prominent than the usual Balmer series of hydrogen. Starting with an A type star (Sirius) will allow you to determine the dispersion which you can then use on subsequent spectra.
IMHO the easiest and best starting point for ANY comparisons is Richard Walker's Spectral Atlas. He presents fully annotated spectra of all the stellar classes - ideal for your needs (and future needs)
(Download the latest English version for the bottom right hand side of the webpage)
http://www.ursusmajor.ch/astrospektr...age/index.html
Hope this helps.
(Drop me a copy of the spectrum and I can assist.)