Being a big Porsche/Volks fan I have to wonder why you wouldn't go with a modified aircooled VW motor,(not that there's anything wrong with the Subie engine), for the sake of simplicity and originality.
No electronics do deal with.
No liquid cooling system..(rad, hoses, fans,overflow etc...).
Extremely easy to modify.
Parts availability..(cheap too).
Going the liquid cooled route you'll have to mount the rad in the front,with the fan(s), and run plumbing all they way to the back of the car...(unless of course you were going to build a front-engined porsche....God forbid).
For a few thousand $$ you can get yourself a real solid, dependable bug engine with about the same HP as the Subie....(and it'll sound like a Porsche too) !!