i was wondering if i could use a 1989 iroc tpi setup in my 91.will it plug in under the dash ok.because the 91 was suppose to be speed density and the 89 iroc has a mass air flow thank you for looking

Yes, you can use the setup. But no, it won't plug right in.
In 1990, GM did yet another wire redesign and moved a lot of wires around. You will have to re-pin some wires on C100 and the C207 as well when installing the engine harness and ECM.
Many people have done these swaps, I'd recommend to search a little and read up on it, you'll find a lot of information on what exactly needs to be changed.

Good luck
Lou