ok so i want to buy this motor but its a 91 i was just wondering can it work in a 87 i know im going to have to get the harness and ecu i got the tack but all i want to know is would it work

YES

If you get all the parts, sure can. The motors swap and fit to your existing tranny..and like you said, you'll need the ecu, harness and either replace your dash harness, or you could try to splice it all. Another option would be to pick up a standalone...it would save the trouble of dealing with the interior wiring.