The reason everyone questions it is even Z1, who made some of the parts you are using, isn't even close. Last I saw, they were making ~350whp in a manual on pump gas and have tested almost every combination of bolt on parts that are made. Also, what gear matters. A 4th gear in a 7AT is 1.412 vs a 1.00 in fifth. Here's a good write up on the various ways you can cheat a Dyno, especially ways the customer wouldn't see. It even covers gear selection.
Exposing DYNO cheaters: how they do it, and how to catch them - PencilGeek's BMW Blog
Everyone here would love to bolt on those parts and get those numbers with a safe tune, it's just in all the years and all the cars the major shops see, there's only been one car that made close and it has far more modifications. Little difficult to believe MA Motorsports, Visconti, Z1, Forged Performance, Jtran, and the other well known Z tuners somehow missed an extra 20-30whp in tuning.