the photo Deuce has posted is not indicative of a t-400 tranny.
The speed-O bullet on a t-400 is in the main case section, not the tail housing
You will need some type of a narrow puller to reach up inside the trans pull off the steel speed-O gear on the t-400 output shaft once the tail housing is off the trans.
I've built a U shaped puller with long legs in the past to pull off metal press on type of speed-O gears. Slip the U shaped around the back of the gear , then thread the puller down onto the output shaft .... the gear slides off. Some times a bit of heat from a propane torch helps the gear to pull off easier.
Dont worry how old you are... it is the mileage on your body that adds up.