Sit Down and Relax!
When we got our 1971 E 27, the previous owner did not have any cabin cushions. I have cut patterns for the shape of the cushions but don't know what the thickness of the cushions were. Were the seats and backs the same thickness? We are getting ready to get cushions made and any info would be greatly appreciated.
You did not ask, but then unrequested advice is all-too-common on the 'net!
Be sure that you make patterns for the cushion top as well as the bottom. They are seldom the same, and only one or two edges will usually be square. If you find a good marine or automotive upholsterer, they will be used to this kind of shape variety.
Back in the day, many builders would put in 3" cushions and charge a bit extra for 4" or 5". Backs would be less, i.e. 2 or 3". Seat backs, expecially when not used as fill-in bunk cushions, will often be an inch thinner anyway.
Nowadays I would put in at least 4" for seating/sleeping surfaces, and use the
2.6 density foam thruout. another way the OEM would save some $ was to use 1.8 density, but they flatten in a few short years. Our denser ones (@ 2.6) still sit and sleep fine without bottoming out a hip bone, and they have been there since '95.
Edit: I should add that all of our inner foam pieces have a layer of fluffy dacron wrapped around them to give them a reall "upholstered (fluffed) look. When you look at them nowadays, they are not flat with odd little wrinkles all over the tops like so many boats.
Cheers,
Loren