I just dropped a 4.11 set into my 55 1st series. It helped that I have the truck completely apart to do the swap. First step is to drain the oil from the rear end. Not sure the right way to do it, but if you just take the rear cover off the diff, the oil will pour out!
Make sure to have a good sized oil pan for that 90 weight as there are 3 quarts of oil in that rear end. After that, you can pull the axles by just removing the eight bolts and sliding them out. No need to take them all the way out, just enough to release them from the gearset. Next you go ahead and remove the 10? bolts that hold the pumpkin in place. Be careful, the pumpkin weighs a ton
and will hurt if dropped.
After you have it removed it is simply a matter of putting the 4.11 pumpkin in place, replacing the bolts, axles and rear cover and filling with oil. It really is that simple
The gasket you need for the rear cover and pumpkin can be found at NAPA (part # P39130).
Keep in mind this is for a 55 first series. I think the 3/4 tons are the same for rear ends but maybe someone else can verify that this will work for your 53 as well.
Good luck.
