The factory service manual
you will need 3 tools , a large pin type snap ring tool , a tapered end flat snap ring tool & a dowel so you can pack 72 roller brgs in the countershaft & hold them in place while you slide the countershaft into the case , I bought the factory tool & made a spare from a worn counter shaft , this dowel will need to be very close to the same diameter to work & exactly the length inside the case so the thrust washers will stay in place as you load the countershaft into the case . The OD version of the 833 is more difficult to build , there are a few tricks & a specific order that things go together to assemble the OD . I have heard of people doing this using heater hose for a dowel but it would not be easy to do .