I got a set of spiffy MK3 seats today and went to swap the bases off some '86 Jetta seats, only to find they wouldn't swap.. THe base itself is a tad wider, and the pins that the back connects too and rests on are closer together.. Pretty much the bases were exactly like my MK1 seats with the adjustment lever on the opposite side.. Did they not change these till later years or something?? I know they were the original seats in the Jetta..
I guess it's back to the boneyard or cut weld and bend to fit...