hmm i was under the impression that the valences would fit the 4dr as long as the 98-01 rear bumper was being used. the bumper is the same, the only thing that changes on the 2dr-4dr are the sideskirts i believe of course i could be wrong. heres a post i wrote up on it awhile back where you can find them aftermarket.post
If you are talking about switching bumper covers then there are obvious issues with getting them to fit. If you are just talking about something that goes below the bumper and the bumper cover stays the same then I don't know why it wouldn't fit, but it might not. I think the 4 door maybe a little bit wider than the coupe, so the 2 door parts around the bumper may not work so well.
definitely no...the two corners of the 4dr bumper (where rear valence is suppose to be) is way longer...i took one of my friends rear valence and try to put it on but nope, the rear valence is too small...
No, the rear bumpers are different. The 4-Door is the same width as the 2-Door. However, the wheelbase is 2.8in longer and the overall length is roughly 6in longer. The front clip is identical, so do the math. If there's 3 inches inbetween the wheels, then there's 3 inches behind the wheels. Ie. The rear bumper is 3in longer (from wheel well to back edge). The valences won't fit. 2-Door bumpers won't fit. Etc. Etc. Check the Helms manual if you don't believe me.