You will need a speedo pinion from a KA powered Hardbody. It will bolt into the tranny in place of the electronic sending unit. They are about $50 and the part numbers are in the Nissan Comp book. Mine is a 21 tooth unit for use with 225/40 VR-16 tires. The stock speedo cable will not reach and must be swapped out for a 300Z unit (or anything suitably long).