Is there any reason a TBI from a 87 Chevy won't work in an 89?

you mean the tbi unit? or the whole system? my engine is out of an 87 (old body stlye) and it went in fine to my new body style 88. i did a howell harness cause the whole trucks wiring had been totally fawked up by the previous owner. but i think all the plugs would mate up.

most plugs will, but the wiring can change drasticly. if you have the diagram follow it rather then what plugs in where.

I should have said that it is a 89 Suburban, so it is the old body style.