F-Bodys have been unibody since the begining.. HP can tweak/twist the frame. I know of people that after HP mods and racing that their T-Tops leak and other issues. It does not take much HP with the f-bodies to twist it.. I have weld in SFC's... But you can get bolt in also and other styles.. Below is just 1 example and its BMR...
http://www.bmrfabrication.com/sfc/SFC001Hsmall.jpg