Neat project, I have done a few various late model EFI/trans swaps though no Hemi's yet. The trans definitely does not need the ABS (rear end) sensor to work properly.

On the speedo issue, you could use the rear end with the sensor and wire in the ABS module but I'm pretty sure you would have to use the instrument cluster as well. The PCM sends all the info to the cluster through two small wires.Speed, RPM, oil, etc.

I don't know whats out there but I doubt if you can get an aftermarket speedo to read that signal.IMO you will need a standalone unit.Good luck with it, keep us posted.