This article by EKWB will get you informed: http://www.ekwb.com/news/233/19/New-revision-od-XFX-7970-cards-brings-compatibility-issues/
XFX changed their PCB layout unannounced a couple months ago, leaving most people with XFX "reference" cards, unable to use reference 7970 waterblocks. You'll have to verify which XFX card you have (EK explains how to do this in the article above). There is currently only ONE waterblock on the market that fit's these video cards: LINK
As for the AM3+ waterblock, I would recommend an EK Supremacy, but if you want to stick with the Heatkiller theme, HERE is their waterblock that debatably performs just as well. Yes, it will fit socket AM3+.