Why not use the cx racing manifold and down pipe?
I make products. Not any turbo kits though. That's not what I do. I make internal and external engine parts, suspension parts, steering components and a myriad of automotive stuff that could be defined as taking something plastic that fails or looks cheap and making it from machined aluminum or stamped steel.
From my perspective the problem with designing anything around someone else's exhaust manifold is if they stop making it, you're left holding your d!ck. You can step up to the plate and make it yourself (been there a few times) or you redesign everything around something different.
Come to think of it, many years ago in the early 2000's I did have some custom exhaust manifolds made to relocate a turbo to work with one of my products. It took forever and the manifolds were all made wrong. They looked great, but they shrunk like a 1/4" because they didn't factor shrink rate properly (this was stainless). Instead of scrapping the parts this outfit fudged all the bolt hole locations inward so they'd line up with the casting better. Of coarse the things didn't fit the cylinder head at that point. It was comically sh!tty. I won't get stuck in that situation again.
I wouldn't much faith in CX racing parts being very good, consistent, etc. In addition, I wouldn't use a 30" long one piece stainless exhaust manifold on a daily driver. That thing will move all over, never hold gaskets and probably crack within 25K miles.
If there a solid, proven cast exhaust manifolds sold and supported by reputable companies for 1FZ turbo apps that would be an option, but you really need multiple sources for something like this if you aren't making it yourself.
For the daily driver turbo crowd the OE manifolds with J-pipes are KISS.