wouldnt be too hard, Removal of glass can sometimes be awkward, and there is limited space whilst working at the lock/handle.
Hardest part would be aligning the door with the hindges. on each of the 2 hindges the bolts wont just go through a perfect circle, they will go through an oval shaped hole. This means the height, and how far forward or backwards the door sits whilst on the car can be adjusted. Aligning the door is a bit of a trial and error thing until you get it right..... just dont fit the door in any old way and slam it to close it as you'll damage the door/rear quarter if it aint aligned properly.
As well as that. Just because your car is diablo red, and this door is diablo red that doesn't mean it will be a perfect colour match to your car. Due to the diablo red being a pearlescent paint, and the cars being painted in different factories or at different times there can be many different shades of diablo red....... as i found out whilst colour coding my old 306... and painting my 406 coupes bumper.
If i park my diablo red coupe beside my diablo red 306 the colours are very noticibly different.
Just a warning. But the door could be a perfect match if your lucky
