the he351ve flange is a wgmt or wgme..something like that, not a T4. yes, you have to build an adapter (i wouldn't recommend welding it to the manifold). or you have to plug the holes on the turbo and redrill.
the 4-2 exhaust manifolds sound like crap..that's why we get rid of them on third gens..plus you'd still have to build an adapter.
catstacks, is that a front main seal leak? looks more like an oil leak from a headgakset or most likely the KDP