The 94-95 style cars lost the black "rubber band" of trim that goes all the way around the car. One solution to your problem would be to fit your car with the painted 94-95 molding and paint the 93 bumper all body color (no black line). Of course, you could leave the molding off altogether if you wish. I'm sure you can come up with a suitable combination of molding and bumpers!
I had a similar problem since I used a 94-95 bumper on my 89. I finally just shortened and rounded the molding on the door. So the black line goes from door to door and around the back bumper. Looks like it came that way. There are some pics on my site linked below.