I have a 88 hatch with a 4-speed trans I am wanting to put in a 5-speed I came across a 91 CRX si gearbox, wondering if this will be an easy swap and what might be needed?

 

Yes, bolt in and go.

 

Just make sure the clutch spline is the same because some have different spline count so you may need the proper clutch for the Si trans.

 

Yes it swaps, you will however need either a clutch disc for an '89 civic or you can go with a complete clutch kit for a '90 - '91 civic which uses a larger disc and flywheel (note that you need a flywheel for a '90 - '91 civic when doing this.