i cant speak for the 2.8, but my 87 had a 2.9. it was a dog. slow, not the best gas mileage, big lack of power, lifters ticked often, valve covers were prone to leaking. engine aside - the radiator in my 87 sucked, i believe Gen I and Gen II had the same (or similar?) single core radiator. I got one from a Gen III 4.0 and never had a problem with it. I'm sure more people will chime in about their thoughts of the 2.8/2.9.
I now have a 98 with a 4L and it's TONS better than my 87. Lots more power, runs better, better gas mileage, no lifter tick, all around a better motor.
I don't know all the details of the differences, but there's some really smart fellas on here that can tell you for sure. just my .02c