^^ Yes, a W58 will handle that power... but you can't slam the gears or do hard launches from a stop and expect it to live. Be nice to it and it will handle it. R154... different story.
Also keep in mind that you're in Cali and 91 octane is the highest you'll have available at the pump. There is a significant difference between 91 and 93 octane fuel in terms of how much power you can get from it as-is.
And in addition to that, just be aware that you've got smog to deal with and even a stock EGR'd USDM 2JZGTE engine will have some trouble getting to 500hp with both catalytic convertors, 91 octane, and the stock turbochargers maxing at 18psi and the issue of a front mount intercooler not exactly being legal these days unless it has a specific CARB number (If you know about "Appendix K" of the smog manual already-- I've looked into this and they want CARB numbers now, which you won't find anywhere for an aftermarket Supra FMIC). The fuel system on a USDM will max at around 500hp I think. Hitting 650hp... that's single turbo, dyno tuning, and E85 fuel with an AEM V2 or ProEFI territory.
Now that said, I've ridden in an 2JZGTE single-turbo SC300 modified exactly to that spec (650whp I think). It was ludicrous. And it was out west.
On the stock-*looking* end you can also try the STU Hagen USDM twin upgrade which can support up to 600-650hp but it's a good $3,000-$4,000 for that particular turbo service and is, again, useless unless you're running 100 octane race gas or E85 with a custom tune. SpeedForSale in Georgia offers that upgrade.
Dotting every "i" and crossing every "T" with a legal swap (which is also expensive-- ask me how I know) you can get 350whp give or take.
Last edited by KahnBB6; 02-26-14 at 12:24 AM.