AspireXVIP

So I'm trying to do some homework on a build before I pull the trigger. I'm trying to LS3 swap my 08 GS350. So I'm wondering how much power the GS 8spd(460) and 6spd(350) can handle. I'd like to keep a Lexus transmission as they are smoother shifting. I know I'm gonna have to find someone to fabricate an adapter for the bell housing. Anybody have any info on this? I've scoured google but to no avail. Any help would be appreciated