The power platforms seem to vary on how much room they take up. 1" is about the minimum and the trucks are way up there.
The Corvette power platforms are about the most compact that you can find off of the shelf.
I used Ford Taurus platforms which I thought were more compact BUT I did do a lot of cutting and refitting of them to the new floor pan pattern. They were not just a simple bolt in.
I can't speak for the Porches, but my Audi TT has power platforms and the car has a lot of head room built into it.
I'm using Hall's Pantera seats with 2" lowered floor pans. If anything, there is too much room.
The saving grace is that these platforms also provide for raising or lowering the seat as well as forward/rearward, rake adjustment and power lumbar adjustment.
Lots of people ignore these as an option because they are the only one who drives the car BUT the cabin of the Pantera is tight. If you are going to drive it for more than a couple of hours it's nice to be able to readjust yourself every so often effortlessly. The power platforms allow this to happen.
I have Hall's recovered Pantera seats that they supply with a manually inflatable lumbar support. It is easily attached to the power lumbar pump in the seat rail assembly.
I'm not sure why so many folks need to go through this, "what seat will fit in the car" deal at all?
Put a Pantera seat in and the thing fits besides Halls being covered in a nice leather and they are very comfortable as well as opposed to the rock hard original vinyl covers and foams?
In any case, I do not think there is enough head room in the car to use a power seat platform without lowering the floor pans? That I never tried.
Some time after 1975, Detomaso installed lowered pans in all of the cars as a matter of course. It's just the USA cars that are cramped for head room.