Can a motor and trans from a 1991 acura integra work in a 1990 acura integra
I can’t imagine why it wouldn’t.
Yes, though there were a number of different engine options, and if you get one that’s different from your current car you may need to replace some other things as well (ecu, axles, etc)
If you’re able to choose your swap motor, stay away from the ZC - great engine but it tended to cook through distributors, and parts are hard to find because it was a very popular swap into the CRX.
Any junkyard should be able to tell you. They all subscribe to Hollander Interchange guide.
Try to bring the ECU with the motor.
For certain there’ll be some minor mechanical differences that can be worked around, but if the ECU is programmed to complement subtle changes to various operating parameters and design changes to enhance MPG or emissions, and these changes are made regularly, that might be the toughest problem to get around. And these changes are invisible.