If you can use a soldering iron, buy the generic 3 wire unit from FCP Groton for $50. Although many warned about the old one being hard to remove, mine came out easy with a 7/8" box wrench. I did use some PB Blaster penetrant, but I'm not convinced that was even necessary.

If your 91 is similar to my 86: after installing, adjust AMM potentiometer so Lambda Sond test point is 50% duty cycle (half time high, half time low) at idle. (pink wire on 2 wire test connector near battery).