Based on what I've seen, I don't think a 92 and a 90 would be interchangeable as I think the 92 has the later tone ring in the diff, so on the front of the speedometer, you'll see K23400 or some number similar to that, and on your 1990 it will have K6380...turn those two instrument clusters over and send a pic...you can't put the 92 speedometer into the 90 if the K-number on the front face of the gauge is different, as even if it functions the speed read-out will be totally wrong.
Sorry I don't know what those extra features are on the instrument cluster itself, but neither has anything to do with cruise control. If you want to add cruise control, you get the speed signal from up above and to the left of the speedometer where that piece of yellow hose is pushed over the 2x spade terminals. I think they put that there because you don't want to accidentally attach the tachometer signal wire there as it can damage the speedometer.