Maybe someone on a Suburu forum would know. The 1.8 engine was the largest offered in the "L" cars.
it depends on how much work you wanna put into it, you could put in any 2.2L or even 2.5L (EJ series) if you dont mind changing wiring harneses and ecu's, I believe you could put in the EJ22 from 90-94 (SOHC) with few changes you get into newer ones than that with the DOHC and wiring becomes something to play with.
Search Subaru Loyale Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Subaru Loyale Experts