If I were to do it (IF... I'm a little lethargic/busy and don't want to disappoint or make promises I can't keep) I would generally ask for track exports of the files (so a wave for each track that needs to be time stretched) at the original project's samplerate/bit depth. These would need to be exported from the VERY start of the project (silence and all) so 00:00:00 to the end of the project. No FX added and exported at a good solid volume.
And EXACT details on the samplerate/bit depth, original tempo and target tempo.
Going from a bundle from an ANCIENT version into a newer version and then back again is just asking for problems. Simple waves can be easily moved back and forth.
All I'd do at that point is set up the project using the original samplerate/bit depth/tempo (oh and time sig... that's important too), perform the stretching/bouncing, export the waves and send them back.
Like I said... I ain't saying I'll do it. Just offering a potential collaborative workflow I've used in the past that works and avoids cross version futzery (this way the work could even be done in OTHER DAWS).
Maybe someone who hasn't had a chance to really play with this type of thing will step up for the learning experience or one of the pros with a little more brainspace and time will handle it. If not let me know and maybe I'll give it a whack.