had the same problem. Crash after installing Mavericks and went back to Mountain Lion. Had downloaded Pages last year and went back to purchases which downloaded Pages 4.1.
Went thru all the standard update procedures but no luck (update pages, "Software Update" from menu and app etc etc.)
Finally I went back to the AppStore to re-purchase Pages and surprise, instead of having "buy" it actually showed "update". After informing my that the current version is not compatible with my OS, I had the option to download an "older" version.
Which resulted in the update to 4.3 - finally ;-)
You might try that approach...