I strongly suspect that your recordings will not transfer as to make a drive work on a different board you have to clear and delete all (including recorded content). You may be able to view the content without a clear and delete but most of the other functionality will be lost.
Darren King will know the full answer and may be able to repair your original TiVo.
If you faulty unit has a functioning MAK this would increase the advantage of repair as with this you could transfer your recorded content to a safer place.