Challenger 6spd - speedo signal?

I'm going to be installing a 5.7hemi and 6spd manual from a challenger into my Valiant and I'm wanting to know how to get an output for my speedo. I will be using one of the speedhut revolution metric speedo's. From what I have read the Challenger box doesn't have a VSS as like the older T56's.

How do I go about getting my speedo to read from the gearbox. I don't want to use GPS, I have read about the magnet systems on the driveshaft. Anyone have any input or done this before - looking for advice and recommendations before I go purchase a kit. Or if anyone can recommend a kit/part number.

Cheers, Dave