86-88 had yellow gauges and round dash vents.
88.5-95 had red/orange gauges and square dash vents. There is no difference in the way the 88.5-89 gauges look, compared to the 90-95 (non-tach gauges/clusters, that is). So I assume you are asking because you need to know if you have a VSS in your cluster. I would guess you don't, but you are going to have to pull the cluster and look, to know for sure.
Just because you have a 1990 dash VIN, that doesn't mean that the whole dash, cluster and all, is 1990. If I were guessing, I'd say they either swapped just the VIN plate to the 88.5 dash and cluster, or they swapped the dash and kept the 88.5 cluster. But like I said, you are going to have to pull the cluster and look, to know for sure.