How hard is it to change ratios in an 8-3/4"?

BTW you asked for the instructions:
#1 Put a floor jack under the rear and raise the car. Jack stands are good for safety. Remove the tires and brake drums.

#2. There are five 9/16 nuts that hold the backing plate to the housing on each side. Remove them. NOTE: On the passenger side, you will find a clip bolted to one of those bolts. don't lose it.

#3. Pull the axles back about 6 inches being careful not to break the brake lines. You sometimes need to tap the backing plate to loosen up the seals.

#4. Remove the U-Joint caps and slide the driveshaft forward in the trans enough to allow it to fall out of the yoke and sit on the floor. Be careful not to let the ends fall off.

#5 There are 10 9/16 nuts holding the "chunk" to the housing. Remove them and then drop the center section. You should have a drain pan under the rear. It may be necessary to wedge a screwdriver between the housing & the unit to break the gasket seal. There are two generally accepted ways to remove and reinstall the chunk. Older guys use a floor jack, but in my day we would crawl under the car with the unit on our chest and "bench press" the 75 pound chunk into place!

#6 Reinstall the drive shaft & u-joint caps.

#7. Reinstall the backing plates and axles. Remember that "clip" on the passenger side that you removed? That is a retainer for the end play adjustment. The bearing retainer on that side is threaded. You can turn it by tapping it with a hammer and screwdriver (yes I'm certain there's a more accurate tool for the job but I've being using the screwdriver for 45 years) Tighten the retainer about 1/4 turn to eliminate any end play (if there is any). Make certain the clip is reinstalled to prevent it from backing out.

IMPORTANT NOTE #1: The older "clutch style" sure grip units had a "thrust retainer" pin that allowed one axle to press against the other for end play adjustment. These pins sometimes fall out when the unit is removed. Without it, you CANNOT ADJUST THE END PLAY! Look carefully into the chunk where the axles go before installing the chunk. If you can see daylight, the pin is missing! Do not install without fixing the problem!

IMPORTANT NOTE #2: If your rear has been modified to run the new "Green bearings" you do not need to worry about the end play adjustment.

#8 Reinstall brake drums and tires and fill rear with new oil.