LS1/Chevelle Trans Options

[mike23109]

I've currently got a Gen I SBC, backed by a TH400/Gear Vendors in my 1970 Chevelle. I'm considering going to an LS powerplant. I know the current trans will bolt up, with some modification or additional parts. I'm considering getting a newer 4 speed auto to replace my current combo. I know I've got several options, however I want something that can stand up to 500-600 RWHP and install without a lot of pounding on the trans tunnel. I anyone running this type of combo? What are you using? What fits?

Thanks,
Mike