in my opinion, there is no need to upgrade anything that is t25 specific, which is why i stated such. you can upgrade plenty of things that are non-t25 specific that will carry over when a turbo upgrade is done so you won't have to redo anything and can still see plenty of benefits from these upgrades. there are many other weaknesses to address before spending $500+ on a tubular exhaust manifold (specifically the fuel system and the tuning of it, among other things), since nobody is going to be making a cast unit.
and chapter 10 in maximum boost is titled "Exhaust Manifold Design," not turbo manifold design. i think Corky Bell knows what he's talking about. go find a turbo manifold for a dsm, you won't. you'll find plenty of exhaust manifolds though. but really it's just terminology, and they're interchangeable, neither one is right or wrong, i just dislike the term turbo manifold