I'd used sti headgaskets on mine, there twice as much money, and messure a little thinner. I went into my engine later on to put new pistons in it, and those sti gaskets compress to the same as the stockers. DON'T waste your time with this issue, its not worth it. I've had a rod bearing spin and just the little bit of space the bearing made cause the piston to slap the head. There's not much room for error when your playing around with your different gaskets.
Just put whats recommended by subaru!