Wanted 280zx 5spd speedo pinion

What year? they changed in 80 but usually you can just cut a new key way and install upside down.

What number of teeth? This determines how accurate your speedometer is in relation to rear end gearing and tire diameter used.

A little checking shows that the 4 speed 1200 used a 17 tooth pinion gear and a 155/80R12 tire with a 22" diameter. If your tire choice is the same diameter (regardless of rim size) a 17 tooth will work.

If running a 23" diameter tire your speedometer will be about 5% lower than actual speed and an 18 tooth will slow it down.