A few people tried various forms of two turbos over the years. There are threads on here from 10-20 years ago on the topic. Search if you want. They never really delivered results worthy of the cost and complexity. You can accomplish the same with a modern, properly sized single turbo as with two separate turbos.
BlueTII laid out the various options using the stock manifold.

 

You also currently have the BNR upgraded twins (using ball bearings and a few more modern bits) and the newer Hitachi 3Kai or whatever turbos.

That will get you in the 400hp ball park, but also an 8374 will easily get there with similar response, that turbo spools like a mad man.

Dale