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I'm sure that even a home built setup is going to cost way more than selling your 300 and buying a 430.
Plus a turbocharged 300 isn't going to be as fast as a 430 with the same reliability and long-term durability. Now, if you want to build a turbo GS300 then that's cool and I sure as heck would love to see it, but it's something you do because you want to have a GS300 turbo, period.
It's as financially silly as buying a 52 year old Lincoln with issues... Oh, wait.