I don't know about the 123 models but on my 115 it requires the removal of the front and rear roof support frame covers (not too hard), the side rails above the doors, and the removal of both the front and rear windshields (very hard and expensive because you need new seals).

If your liner is 30 years old as mine is the window seals probably need to be replaced anyway. If you go this way read mine and other's threads about installing these windows. Not for the feint of heart.