...would they fit in a 1991 240SX hatch? I'm thinking about buying some and putting them in my 240

 

not without a customized/custom seat rail.

the hump in the floor is what keeps most seats (universal or otherwise) from working with the car.

You'd be better off buying S14 seats and recovering them.




And FYI, S14 aren't "bolt in" to an S13 per se. 3 of the 4 holes will line up perfectly fine, but to get the front left hole to line up, the tab must be bent downwards. That's easy enough to do however, because you can just use the bolt to angle the tab down until the bolt meets the hole, and then you can just tighten it down as normal (the action of tightening the bolt will seat the tab).