Can I copy the OS from a non Premier XL

I have a premier xl with a dead hd. So far have not been able to copy the HD because it is taking too long. My sister has an XL with 4 tuners and a few other tivos as well but I can't get a straight answer on which exact versions she has.

Just wondering if I could copy the OS from another tivo premier non xl or what I can do to get this tivo working again?