factory service manual ... but you need a later manual for the 75 up OD 833 , the OD is a different animal , the larger OD gear on the mainshaft will not go into the case unless the countershaft id dropped down in the case , so you need a dummy pin to load all the brgs into the countershaft & hold them in place while the counter shaft is lowered , then you need to insert the mainshaft & rotate the tailhousing 180* I slide in the countershaft pin once the countershaft is positioned then rotate the tailhousing 180* back to the normal position & bolt it on