Personally I found the fitting was pretty straight-forward, apart from the fact you may have to drill out the rivets on the drum casing as my unit was riveted shut. They supply a new drum usually which you will need as the wire seems to wrap itself up in there and wreck the grooves on the drum. Also some of the bolts had rounded off, i presume the previous owner had it fixed once.
The tricky bit is getting the window level, tilted in, sealing against the car etc.
First time the work took 3 hours, as I didn't know what I was doing, Next time took about 1.5 hours..... Setup took another 3-4 hours both times. The third time it broke I took it to the Indy to fix it as I couldn't be ar$ed with all the gaffing around endlessly adjusting adjustment screws you can't see etc.
In fairness though you might find it easy, depends on if you have to remove the whole assembly.
wattsie