Doing a clean install of Mavericks and installing iWorks 09 and the new iWorks for OS 10.9x
Or if it feels safer:
1)  make a clone or Time Machine backup of your current OS before upgrade. 2) Once you have the clean install working effectively, make a copy of your previous OS clone (call it Clone2)
3) Mount Clone 2, delete all applications except iWork 09 (and any others you want to port). 
4) Open Migration assistant and check 'Applications' only. Commit.

MA will now copy iWork O9 and its preferences / key to the new OS without affecting anything else.

Caveat(s): 
- This may overwrite iWork preferences for a later version - but generally not on Apple as they are named differently. For example, I have 4 versions of Apple iMovie on one of my Macs for old projects. 
- Bear in mind that porting an older programme over does not ensure that it will run well on the new OS. Make sure that the two are compatible first (forum search). There may be a soft hack to resolve an issue in some cases. For example, I like to run an older version of 'Text Edit' (with zoom control) from 10.6 under 10.8+ although I have to use a command line control to turn off its auto-save feature as this is now done through the OS. Without this it has a constant nag message 'you do not have permission to save this file'.