non turbo shortblock in a turbo Impreza
 

Can it be done? Higher compression I realise but who is to say with turbo heads it would not be fine with mapping? Opinions?

I think Boosted has done this

Can be done then

the block itself is the same, but not internals.

AFAIK what boosted did was use the block and change all the internals (this is the same as what I'm having done right now).

What are the differences?

The block itself has no difference AFAIK.

The pistons will be different - not sure if the rods are different between WRX and NA (the WRX ones look pretty flimsy, so who knows if they use the same rods in the NA as well)...

oh also the crank is compatible too.

Not sure if it's got all the same oil feeds etc, mind. I know some STI cranks have improved oiling, but don't know if there are NA / WRX differences (I doubt there are any differences, but can't say for sure).