As Dieseltech has said it will be necessary to remove the shifter cover and/or the hydraulic cover if either tractor has MP. It will also be necessary to remove the LH side cover in order to align the splines for the main drive shaft and main hydraulic pump. The main shaft and shear tube can be put in afterwards. It is certainly advisable to remove the split pin from the shear tube to ensure correct position via the correct splitpin hole in it.
On going that far it would also be advisable to remove the hyd cover of the back end to be used to clean the filter/s and remove any buildup of grease that may find its way into the filters from years of greasing of the cross-shaft.
DavidP, South Wales