You have a drain plug on the very bottom underneath the driveshaft enclosure. If you are going to drain it that is the time to do the side gaskets. If it has never been drained there we be some nasty sludge in the bottom you may want to flush it w/kerosene once the side plates are off. You refill through a plug about 1/2 way up on the passenger side this is also the level control, when it trickles out of the open hole you have it filled. As I remember it was two quarts and then some from a third after a complete drain. If you use the bottles with the top that can be cut for flow you can angle that into the hole to help fill. Pull the trans cover inside the cab and it is a bit easier.