Wotcha and welcome STI will def not fit, different wheel bearing housing size. WRX-S may fit - an exhaust for teh WRX s fitted my NA 2.0 with a different sized O seal required as the manifold dia is different
Would a set of lowering springs be a reasonably cheap first step?
Wotcha and welcome - few XV owners on here, not sure about the subaru diesel option though, unfortunately it is not a great product and the Fozzy diesels have many issues. Is a petrol option completely off the table?
Have you thought about a legacy if you need the estate type setup?
for example
https://www.pistonheads.com/classifieds/used-cars/subaru/legacy/subaru-legacy-2-0-twinscroll-bl5-turbo/10093453
try this
https://www.ebay.co.uk/itm/Subaru-Impreza-WRX-STI-2004-2014-Haynes-Workshop-Manual-89080-NEW/202820981553?hash=item2f39129331:g:UAEAAOSwv7ldyvlp
Surge tank kit assembled and mounted, next bit will be electrical string & relays plus fuel pipe
Test fit
Trimmed, drilled and bolted down
I may add a layer of rubber or part of the boot liner, post cut, for pump vibration isolation