It's quite easy, just follow the workshop manual instructions, the balls retaining the shifter shafts will tend to roll out but a screw driver down the shaft will soon push them back in. The main thing you need to do is replace the O rings with quad rings QR112 I.D 1/2 inch O.D 11/16 C.S 3/32 they will fix the oil leak. You may find the locking bolts for the shifter folks may snap when you unscrew them so you will have to carefully drill them out and fit new ones, all good fun.
Graham