the speedo sensor it's easy to change. It's on the left site of the transmission near the CV Joint flange. You need to remove the 3 pin connector and unscrew the sensor.
If they speed and reference are seized in their bracket it's a pain to get them out sometime. I think the easiest way to get them out it's to try to remove the whole bracket and then remove the sensors from the bracket. You need to pay attention when you install them back. There is a detailed procedure about setting the gap to flywheel on
Clark's Garage Home Page