Use the Fire emulator in the (free, downloadable) KIndle Previewer?
A mobi file as built online through the KIndle Direct Publishing platform (and I think also using Kindlegen or Kindle Previewer) actually contains two files, one for KF8 devices and the other for KF7. (KF8 is being extended to earlier devices through firmware updates, although the results aren't always the same.) When a customer directs a book to his device or app, the server sends him the correct version for that device/app.
But perhaps I misunderstand your question?