Will the round style plastic that mounts to the dash and houses the instrument cluster bolt on to my '89

 

yes, but might not bolt in the right places underneath and might not fit right
there are many differences between 88-89 and 90-91 civics, guage cluster and bezel are one of them, you might be able to make it work but i think it would be noticable, and i've always been a fan of the small square guage cluster setup in 88-89's
if you get creative and fit the bezel up to it well anyways, let us know it could be cool

 

Thanks, I'll give it a shot.