To do the manifold correctly for a true divided turbine housing like the gt42r has, you need to analyze the firing order of the engine.
The firing order of the 2JZGTE & 2JZGE are 1,5,3,6,2,4.
You then send alternating combustion events to each side of the divided collector. So for the front half of the divided collector you feed with cylinders 1,3,2. So for the back half of the divided collector you feed with cylinders 5,6,4. You need two wastegates, one for each side of the divided housing. This completely divorces the front 3 cylinders from the back 3 cylinders, turbine efficiency and response is increased. This is how you're seeing honda B18's making 30psi with the GT42R at 5500rpms. I'm not sure what the difference in spool up on a 6 cylinder is, but 4 cylinder guys are seeing 500-750rpm quicker response.
Justin
Justin