Dont think there is a diff mate,
I managed to fit one from a mk2 to a mk3 and vice versa. best way to find out is to try and see
easy job to do:
1. unscrew behind the steering wheel to take off horn cover
2. remove spade connector from horn cover (has wire attached to complete the electrical circuit when you press the horn)
3. unbolt the steering wheel from the barrel (its a big bolt-around a 19mm if i remember correctly)
Craig
EDIT: reverse the above procedure to put back on