I'm definately gonna make new manifolds as that's the most significant part to reduce lag and increase power. Also the front manifold will curl up while the rear one goes down. I got 50% of the parts so not much farther to go.
I got no prob makin a collector, and I got all the equations from my school books, so no probs there, although I did forget to take intto account the gases cooling ... And solidworks FTW cause you can print off the profile to cut
And I didn't know about substrate cats