Yep. The 87 an 90 samurais are wired slightly different at the instrument cluster plugs/connectors.
You are correct, in that a 90 samurai would have had an EFI engine.
The cluster can be rewired to work. I have rewired an 87 cluster to work with a 91 wiring harness/engine, so I know it is possible. On mine most wires just needed to be rearranged in the connectors, although I did run a new wire and do some other minor mods. The best thing to do is to get a wiring diagram for both years and study them thoroughly.