There's a couple out there, but unfortunately no GT15. As my Turbo TR1 will only be used on the dragstrip, I will just suck it and see how long it really lasts, if you don't overfuel it, it should work out a few seasons in my case and maybe by then, someone, somewhere will have a carbon seal setup for the GT15.
That being said, you have heaps of space, just go blowthrough with the stock CV-carbs. It's not that hard - shoot me an email and I get you some literature/links to start from and help you get into it. The only two additional things you'll need are a fuel pump (can be sourced from a big-displacement car directly from the breakers and an adjustable fuel-pressure regulator, where I'd advise you to get a proper Malpassi as these are the de-facto standard on carb'ed turbo builds and you'll easily find some setup advice should you need it.)
It would also allow you to go down the intercooler route in the long run to help you keep the charge cool(-er) and thereby allow you to run more boost.