I must agree that one of the most aggravating tasks is replacing the duct tubes on a completed Healey. Bending over the fenders and trying to get appropriate leverage and hold during the install is even more frustrating as I get older and loose flexibility and strength. A few years ago, when installing my bilge blower for an article I was writing, I removed the front fender and the task was a cinch.
Yes, removing the fender seemed to be a greater risk then working only under the bonnet. However, removing the fender and door (after marking the location of the hinges) took a casual 1 1/2 hours and reinstalling it was not much more. Assisted by better leveraging position, the installation of the Duct was quite a bit easier with the fender off and I was able to easily do a number of other things as well with the easier access. Although I did not do my heater duct, I could see the same, if not more, benefit derived when removing the right fender when doing anything having to do with the blower or duct. Although this is how I addressed the issue and leave others to make take their own approach, it did work well for me an sometimes doing more turns out to getting something done faster and will less overall effort.
Ray(64BJ8P1)