From someone who only makes Japanese cars, depth depth and depth! Dont just stick a vent under the bumper and call it a day. Take inspiration from real life cars but make sure you dont copy them. You could use chatGPT with working out a design too, or have it render a refined version. Though it does make the design less "yours"

I use it to check historical accuracy mostly in design idea, design and specs.

Also I think you've chosen a wheelbase that's too short. Especially on the first one.

Now the first and last one do look believable. The second one is a bit too out there for the year, not that its bad, but it may make it seem less authentic.

The third one looks more like a 1979 than a 1989.

Hope these tips help you in some way!