My c body blown 450 project should scream with mega torque. Will I need to stiffen my chassis? How do I go about this?

 

Hard to say.....

 

A good start is welding in torque boxes and some subframe connectors. Auto Rust Technicians has all that stuff, decent quality too, I've used their b-body stuff before. Unibody constuction is pretty stout as-is, unless it's a convertible anyway.

 

A 6-8 point roll bar with X's in it will help a lot
A buddy of mine picked up 4/10ths just being able to drive the car out on the other end without his butt sucking seat cushion
He did the connectors & boxes with 2X3 square tube connecting the rockers more solid the 1st time There's a lot of flex there even after that

Watch how far the underhood braces move & when you remove them because they don't look cool. it flexes even further

You attach the quarters at the door jamb area as high as you can on the bar & run braces up on the firewall that tie into the front legs at the floor
Have your doors in perfect adjustment & open & close them as you do this so you know there's no problems with them when you're done