Replacing Speedo Gear in 904

Hey there.. Im new to the mopar world and just brought a AP6 with a 318 and 904 transmission. My question is my speedo reads about 20 mph out. Im assuming given its a mechanical drive that its got the wrong speedo gear drive. How easy is this to change, are there any special tools required to get the gear out and swap it.. any tricks I should look out for. Any advice is much welcome..

Cheers
Author: AV8AP6