Originally Posted by john 1badSTI
The blocks are interchangeable to a point I think the outback block is open deck where the sti block is semi-closed deck.
This is the only real difference, besides the heads. That really doesn't matter though since your doing a hybrid build. You could buy the block and have a closed deck plate machined for it anyways, that's what I'd do.
On the other hand don't use STi pistons, the rods though can be had rather cheap and are good for like 500whp or some **** like that. It's just worth the money to buy some forged pistons though. You'd have a built 2.5L for like $800 if that.