How far does 400hp get you in street racing these days? Are you racing for pinks against minivans or what? :D
For whatever its worth, the local (very well liked), restoration shop that bent up the exhaust for my car said that subframe connectors are pretty much mandatory for stick shift cars while automatics are typically ok for mild performance applications up to a point. He was pretty insistent about it and discouraged me from bothering with my 300hp/400lbft crate motor. This guy has a gorgeous '69 Charger R/T, a '68 Barracuda 383, another with a 340. His son drag races a '69 Superbee and drives the wheels off of his '72 Roadrunner. These are Mopar guys...so in most cases, I tend to take their opinions seriously. If your car is relatively fresh/low miles...maybe he's right. After all, these cars weren't slouches from the factory and most guys didn't bother with this stuff back in the day as far as I know. Then again, tires were way less sticky back then. :D
Personally, this is one of the few areas where I think they're underestimating the importance of bracing. I believe that any smartly-placed chassis reinforcement is worth its weight in gold-pressed latinum. Chassis flex is bad for handling, bad for the driving experience, bad for the car. 400hp is a lot for a ~50 year old econo car chassis.
