good question

 

The 98 and 99 RS are identical except for a few things. 98 had an L/canadian style front bumper with smaller foglights whereas the 99 had a WRX version 5 front bumper with larger foglights. The 98 also had frosted headlights whereas the 99 had those nice clear headlights. And finally, the 98 had gold 5 spoke version 5 WRX wheels whereas the 99 had the same wheels in silver. I think that is about it.

If you were to purchase a 98 and wanted to convert the front bumper, you would need new foglights, foglights brackets, bumper skin, bumper beam (it is a different size), turn signals, and the little orange vents. All can be purchased for ~600 from a subaru dealer, but you can always purchase parts used such as the foglights and the beam and save a ton of money.

Just to give you an idea of the cost breakdown of parts purchased from a dealer, the bumper skin is around 160, beam 185, foglights around 90 each, vents 20 each, brackets 10 each, and turn signals i am not sure, maybe 20 each. Like I said, beams can be bought used fairly easily for as low as 50, and foglights as well when people are selling them every now and then. You could alternatively purchase Hella 500 foglights, which are quite popular for around 50-60 for a pair. One thing to note though is that you are pretty much stuck purchasing a bumper skin and having it painted since the chances of finding one in good condition coming off of 99 RS the same color are VERY slim (I have tried for a very long time to find one myself).

Some links for you:

Subaruparts.com complete bumper assembly (washington dealership)
http://www.subaruparts.com/catalog/?section=167#1110
individual part numbers for bumper related parts (do a word search)
http://www.ravensblade-impreza.com/p...tsimpreza.html