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This may have been covered at some point, but despite searching the suspension sticky, I'm still not sure if there's a way to figure out what I'm trying to figure out...
My dilemma: I have a complete set of WRX struts and coilsprings to replace my really, really beat old ones. The trouble? I'm not sure what year the car was that they came from. I *know* it was either an 03-04 but, apparently there are some differences concerning which parts I need to purchase to make the retrofit -my car, incidentally, is an 90 LS AWD na w/o the air suspension option)
Is there a decent resource for determining which parts I have? A good online catalog for searching part numbers or how to accurately read said part numbers?
I need to do this project immediately so any assistance would be very much appreciated.
Thank in advance!

Are the wrx springs tapered in the rear? If so, then those are from an 04. If that is the case, you aren't going to need anything to get them to bolt up.

Seeing you have a 90, you can use your current rear strut top mounts for the rears on your new struts, so basically you need to purchase nothing to get these to fit.
If you have the complete set, the fronts should bolt up without having to use any other components, which is, assuming you have 04's.
03 wrx, I really am not 100% sure about the differences there.