the AWD system is in the drivetrain. it has nothing to do with the engine.

personally, id do the crv awd system. beef up the rear drive axles. custom crv manual tranny with itr? ratios.
for the engine, mdx 3.5l engine with cl type s heads.

if the v6 is out of the question, then id say a b20 w/ a b18c5 head with all the internals for boost, and then a fat ass turbo on it.