If you do that, don't cut off the old terminal that goes in the big round connector. Splice in just behind it and put a sleeve or tape over the exposed terminal, so you can use it again in the original configuration when you get the correct cluster for this car.

There really is not any interchange to speak of over the years with electronic speedometers. The 91 cluster is the same with or without ABS, but it is different from a '90, and different from a '92. Unless you are into detailed mods or don't care about some features (e.g. ABS and warning lights) the best approach is to have the correct year cluster.