The R50 cat mounting on the exhaust manifold has a large (about 5" or so) opening that bolts directly to the manifold with 6 bolts. It comes out the back of the manifold, then goes to the exhaust.

The X manifold directs the gasses to the middle of the manifold, then goes out a normal sized hole to the cat (about 2½" or so) with 3 bolts. The cat then runs down to the rest of the exhaust, front tube expansion chambers, etc.

I don't think they'd be interchangeable at all. The Pathy unit would need the Pathy cat, the X header wouldn't be able to adapt to the Pathy cat due to space. The Pathy header might be able to get adapted to fit the X cat, with an adapter, but it wouldn't fit in the X space either.

Looks like totally seperate pieces would have to be fabbed up.