Mikey, I have never done one, but looked close at a number of them in person. Yes, they are lame, yes L-A-M-E but engineering marvels.
I opened and closed one a number of times at SEMA just watching it work, I'm easily entertained.
They look straight up bolt on, as far as the ones I saw. They bolt right were the hinges mount and seemed to "work" as best as you could imagine for something that is TRYING to change the design from the factory so much.
The "hole" the door closes into is just not designed to work with the door moving in this direction, so of course the "lambo" doors really aren't "Lamro" style, but a sorta close counterfet. The door opens OUT, then up, and closes down, THEN in. If you don't do this just perfect things hit, that are not supposed to hit! In other words, if the owner doesn't pull the door down correct and it comes in a little as it comes down, WHAM it hits the quarter. If you blow up photos of cars with these doors you may be able to see the chipped paint around the doors and jambs from them hitting. Almost every car I have looked at in person had these chips.
That all being said, make sure the customers expectations are low, that he doesn't expect YOU to make these things work perfect. And give a super ball park with a time and materials bid.