Well, the thing here is:

The transmission in a '90 loyale is essentially the same thing as the transmission in a '92 legacy, an '85 brat and a '96 WRX. The only things that change are some linkage elements and (obviously) clutch systems. If you fir it with the proper clutch and can properly mount it, I don't see why it wouldn't work. Granted I'm no transmission expert, my word should absolutely not be taken for truth, merely speculation. Subaru has been using the same five-speed for about twenty+ years. Their first all-new manual transmission came with the new WRX STi.

-adam