That's strange about the sander pad getting hot. The triangle head (detail sander) for my HF unit is basically thick foam rubber and I have never experienced it getting too hot.
It's great you got that wing covering off without damaging wood.
Regarding fuselage differences between 1400 and 1550, you can always drag your fuselage up here and we can compare them side by side. I think since we met Nate we know where to look.