Not sure about the plugs, but the shape is also different. Specially towards the gas and temperature gauges.
Well one difference that sticks out to me is the 99 has the digital odometer and the 97 has analog. Not sure on a retrofit but looks like not worth the hassle because of differences.The trip meter reset button and a few other items have quit working on my 4runner. Will the cluster from a newer 3rd gen work in it? Are the plugs different?