Use a Premiere 500GB HD in a 320GB Premiere?

I have a Tivo Premiere TCD746320 (320GB HD) with a lifetime subscription. Can I take the hard drive out of a Tivo Premiere model TCD746500 (500GB HD) and use it in my unit? I am looking at this as an alternative to buying a blank hard drive and going thru the software copy/transfer routine.
--thanks--