I am building a 89 sei trans for a 5speed swap. But with riseing fuel costs I want as many mpg's as possible. The 89 sei has a 4.066 final and the lx's will have the 3.8 final. I already have it apart so I will try to replace it now. I say again final drive is not 5th gear. The final drive is the matching set of the main shaft and the ring gear. Thanks Mike C.