Changing coupler location is of course the secret. You want to pick a minimum radius, try it with two cars, then convert your fleet. 74" radius is not quite enough for me to run an SP articulated coach with correct spacing. I had to add a sixteenth of an inch.
From my limited diaphragm experience, I think paper is the best. I use metal strikers and paper bellows. Cloth works well for full width diaphragms, but I only use those on articulated cars. Both hold paint well.
I have had zero luck with rubber diaphragms. Their shelf life is quite limited.
