My opinion is that if it's a small bumper, it should stay as a small bumper.
For some reason, if it's got a reg plate older than G reg, it just doesn't look right with big bumpers. G reg cars can go either way as that was the year they changed over.
If you're gonna complete the post 89 look, then you need to swap your front doors with quarter lights for ones without quarter lights and wing mirrors in the corner of the window.
But that's my opinion. It's your car, do what you want. (Within reason and taste)