its not hard at all i have done it on mine (k11 1997)
basically the manual and electric mechanisms have the exact same attachment points to the door so its a straight swap
then you have 2 wires coming from your motor,
at this point i did a google search and got my head around how electric window switches worked (how they reverse the +ve and -ve for up and down functions, its quite clever)
anyway once i got the jist of it, i went to a scrappy and robbed a random car of 2 switches which were attached to the same piece of electrics
then i spent ages with the multimeter finding out which pins on the connector for the switches did what (eg, +ve input, earth, left door up, left door down, right door up, right door down)
then run your wires, solder it all up nice and neat, and locate the 2 switches in between the driver and passenger so you can both access them
i located mine in front of my sunroof wonder and they look cool in the roof