Yes they do fit, I have them in my '91 SE-R. Unfortunately I can't give you any details on the swap because I purchased the car this way. They are a nice touch, black leather, and certainly make you feel like you're riding in something a little bit nicer
One thing though, the front driver and front passenger seat belts don't click in very easily, perhaps the P11 female seat belt receiver is a bit smaller as it takes a bit of shimmying to get the B13 seat belts to click in.
I'll take some photos later today and post them in here. They look great, and the rear P11 seats have a center arm rest that can be pulled down as well.
edit: it was pointed out I actually have P10 seats, photos below. sorry for confusion