Originally Posted by Marnix
The block will be roughly 2 mm less wide with the thin gaskets therefore the manifold won't line up. You can drill out the holes in the manifold though to make it work but why would you want to do so if you end up with a too high CR anyway? Besides, the ports of manifold to head will also be off (by 1mm per side).
Besides those issues you will also have to use the latest belt tensioner setup with the extra idler when using the thin gaskets to prevent belt slack. With the thicker gaskets you can use your original setup.
I agree on the tensioner setup but continue to disagree with you about the manifold geometry.
This build I did was for a US 98 Legacy GT, it had an EJ25D in it. We ditched the shortblock for an EJ257, I rebuilt the heads and we used EJ257 OEM STI headgaskets and I 5hit you not, intake manifold installation was smooth. No hogging holes out or drill bit wiggling was required. True story.