What is the deference between a 1990 Honda prelude and a 1991 Honda prelude?

Can I do a motor swap with my 1990 Honda Prelude with a 1991 Honda prelude? Both are b21a1 2.05L engines

Yes you can, it will be a simple plug and play direct swap with little of anything needed other than fluids. Don't forget to change the clutch and resurface the flywheel. It's much easier to do now than have to pull it back out to do it again. (Unless it's an auto)