'89 crx si seats

how much modification would it take to put 89 crx si seats in a 91 civic hatchback dx?

Much more trouble than it's worth. I just traded the set of '89 CRX Si seats I had for a set of '90-91 h/b Si seats (to put in my '90 h/b). It can be done, but you'll need to have two of the rail mounts rewelded in different spots.

The CRX seats are about 2" wider than the hatch seats... Like I said, it can be done, but IMO it's easier to just get h/b (or Integra) seats...