I'll take a few minutes and explain what does and does not work in the second generation Legacys (BD, BG, and BK chassis codes).

OEM Subaru Strut / Spring Swaps :
  • 2002 - 2007 Subaru Impreza WRX
    Any WRX setup in these years wagon or sedan will fit any second gen Legacy. On some combinations, you may get whats called "*** sag" or a "saggy butt". This is cured by using 3/8 inch spacers. You can make your own, or there are a few places where you can order them online. I believe Paranoid Fabrications makes sets of them. I had a set that was made from a kitchen cutting board and they worked just fine.

    This setup will get you a little bit more of an agressive spring rate while not compromising ride quality. You will still experience some understeer and body roll if you're on stock sway bars. For a daily driver with occasional aggressive driving, this is an EXCELLENT upgrade. Especially if you never plan on competing with your car.

    You are able to use just the WRX spring on your current Legacy struts, but you will need WRX top hats as well. Even though this is not possible, its not recommended. You will wind up with a sub-par suspension setup.

    The one difference between the Legacy and WRX (and STI) suspension that you will notice is the way the brake lines clip to the strut. There are two ways to fix this. If you want to keep your current brake lines, you can zip tie them to the strut. If you want to do it the proper way, you can buy 02-07 WRX brake lines for all 4 wheels. This is an excellent time to upgrade to stainless steel brake lines.
  • 2004 Subaru Impreza WRX STI
    The ONLY STI setup that will bolt right up is the 2004. In 2005 and up, Subaru changed them to 5x114 hubs, so the later struts do not fit. This is basically the same as the WRX suspension info.

    You are able to use the 05 - 07 STI springs with either your stock Legacy struts, or WRX struts though. STI springs on WRX struts usually isn't a bad upgrade.
  • Second Generation Subaru Forester
    The Forester suspension will lift up your car about an inch over stock 96-98 Outback ride height.
  • Second Generation Legacy
    Any 95-98 Legacy L, Legacy Brighton, Legacy GT-B, Legacy GT, Legacy Outback, etc will swap suspension with each other.

    Please keep in mind though that the Outback has 2 inch body spacers in it to keep the CV angles correct. If you're lowering your Outback, be sure to remove these. If you're lifting your non-Outback, be sure to add them. Along with the spacers, you have different sway bar brackets as well.
Coilovers

Your options for coilovers are virtually endless. Finding coilovers for 95-98 Legacys is going to be near impossible. To get MUCH more options, shop for a 02-07 WRX since those setups are a direct bolt on swap.

Stay away from cheap coilovers. You get what you pay for. Personally, I wouldn't spend less than a grand on a set of coilovers...and even then I'm still picky on what I get. My last set was D2Racing and they carried a price tag of $2300...but they were amazing.



Swaybars & Endlinks
Anybody thats looking to make their Subaru handle better, this should be one of the first things on their list.

To sum it up, swaybars help prevent body roll...and a bunch of other good suspension geometry stuff. I won't get into that in this article. I'll keep it simple for now.

Here is a list of what will fit on your second generation Legacy (compliments of Jamal on SLi)

Turbo Front
Legacy
91-94: 18mm
GC WRX/STi: ?
02-07 WRX wagon: 20mm
Non-turbo Front
Legacy
90-94: 18mm (19mm air suspension?)
95-99 2.2: 19mm
96-99 2.5: 20mm
Impreza
93-01 L sedan: 18mm
93-97 Wagon: 19mm
93-96 LS: 19mm
OBS: 19mm
98-01 RS: 19mm
02-07 RS/TS/i: 20mm
Tribeca: 25mm
Rear
Legacy
90-92 non-turbo sedan: 16mm
90-92 non-turbo wagon: 17mm?
92-94 L: n/a
92-94 LS, LSi sedan: 16mm
92-94 LS, LSi wagon: 17mm?
94 Ti/GT/Mi: 17mm?
91-94 turbo: 18mm
95 (all): 15mm
96-99 2.2: 15mm
96-99 2.5: 16mm
95-99 outback: 18mm
Impreza and 00+ Legacy bars do not fit.
Whiteline Aftermarket


Turbo front
BSF18 - 20mm
BSF18X - 22mm
BSF20Z - 22mm adjustable (22-21)
BSF20X - 24mm
BSF20XZ - 24mm adjustable (24-23)
BSF20XXZ - 27mm adjustable (27-26)
Non-turbo front
BSF19 - 20mm
BSF19X - 22mm
BSF19XZ - 22mm adjustable
rear 90-91
BSR17 - 18mm
BSR17X - 20mm
BSR17XZ - 20mm adjustable
rear 92-99
BSR19 - 18mm
BSR19X - 20mm
BSR19XZ - 20mm adjustable
BSR19XXZ- 22mm adjustable
Other Aftermarket
Rallitek - 22mm non-turbo front bar
Addco - 1" F, 7/8" R
others?