They did update the block, that is why it isn't a 4.6 anymore.
My brothers normal '11 GT is rated at 400 and some odd hp, throwing more power at it won't help much, it can barely contain what it has. Just a tune makes crazy power with the variable cams, and blower kits are just now starting to come out for them as well. Not that is underpowered by an means originally, you can leave two black marks as long as you care (at $300 a tire it doesn't take long to care).
The Boss 302 (like the original) is set up for road racing and high-rpm running. So they just set up the 5.0 to run at extended periods at high RPM and reworked the suspension to improve handling. It isn't meant to contend with the caveman-with-a-club GT-500.