Although I appreciate that taking off the wing is a pain that many will not even consider, I find this removal will makes your task faster and so much easier, in total, then doing the job with the wing in place.
A Side Story
Way back in 1968 when my Healey was my daily driver, its defroster was so insufficient that I often wondered if it was a planned practical joke. While visiting a salvage yard with a friend, I spotted a 1961 Olds Starfire Convertible that had been in a major accident with its blower easily accessible. Expecting that this convertible’s blower would be much more efficient, I purchased the unit at a good price for the motor alone as the blower case was smashed.
Returning home, I pulled the wing and extracted my original heater blower and extracted the motor by opening the case. Adapting the Olds motor to the Healey’s blower case and squirrel cage, I reinstalled the unit. When turned on, the defrosters transmitted a much greater volume of air to the point that it whistled. In the car, the unit looks and operates as original but now the defrosters are no joke and clear the windscreen.
Good Luck,
Ray (64BJ8P1)