Mostly what we do here at Crawford requires us to buy brand new OEM short blocks direct from Subaru. 9 times out of 10, we replace the stock pistons with forged ones, and long story short, we end up with a bunch of brand new OEM take-out pistons.
In order to get you the correct pistons, take a look at the block you intend to put them in and on the top of the casing there should be a stamp telling you which sizes you need.. either 'A' or 'B'. Looks something like: AABB or ABBB, etc. Wristpins included. Rings sold separately.