Thanks to Dave at Legacy Central for these wonderful articles.
1990 Legacy Press Release - This is the initial press release when the Legacy was first introduced in 1990. It talks about all its features, specs, and not to forget how three production level Legacy RS's broke the World Speed Endurance record with an average of 138.78 mph for more then 18 days and 62,000 miles!
1990-1994 Legacy Parts Sheet - This basically gives you a complete parts list of the entire legacy, what their Subaru part numbers are, etc. Extremely helpful, exploded diagram views. The only thing it's missing, if you could say it's missing anything is exploded parts list for the engine.
SAE Tech Article on the new "Boxer" engine - This article has SO much technical information about the new "Boxer" engine. It has hp/torque curves, talks about all the different intricacies of the new EJ22 for the states and the EJ20T for overseas market.
Here's some more excellent tech info. I originally got them from FinleyWeb.Net. They weren't the easiest to browse through or find information, so I have added bookmarks for all the headings and structured it in a way so information is a lot more accessible. I've put the index/bookmark structure in a word document. You can download it here.
1990-1994 Subaru Legacy Parts Catalog (Full) - This is the official Subaru parts catalog for the 1990-1994 Legacies, with diagrams & part numbers. This is the entire catalog!
1992 Subaru Legacy Factory Service Manual (Engine & Wiring) - As the title says, this is the Factory manual for the 1992 Legacy. These scans only contain information on the engine & some wiring.
1992 Subaru Service Bulletins - These bulletins have a lot of good information. It's not just for the Legacy. There's information on the SVX, Justy, and older Subaru's. Check out the word document for more info on what's in these service bulletins.
Miscellaneous Subaru Manual Scans - These are various FSM & Chilton's scans I have done over the past few years. Feel free to browse through them.
1990 Subaru Legacy Owner's Manual - Someone asked me for this a while ago, so with a little patience on my part I have scanned my entire owner's manual. You can browse through individual images or download a pdf file with everything in it.
BC-BF Sti Parts List - This site had been floating around. I decided to mirror & convert the site to English. I'm not sure if the part numbers are still good, if not, the new ones should automatically supercede the old ones when entered in the Subaru parts database.