I am going to be ordering a set of US Car tool frame connectors with there torque boxes. I am also looking into there rad support upgrade. I am using the car only on the street with 600hp. Has anyone used there rad support? Is it worth the investment? Or will the frame connectors and torque boxes be enough for what I am planning to do with the car?

I installed their radiator support in my E-body. I am not very impressed with it and would look to the XV version, if they make it for an E-body. Just depends on what you intend to do with the car.

With that much on tap i'd suggest more reinforcement even if your only on the street. Since you don't need to follow any sanctioning bodies rules welding the body seams is certainly a good upgrade. Front fender braces are a nice plus too! Can you weld? What tire sizes?

I am going to get someone to weld the frame connectors and torque boxes. BF tire 275/60/15.

Guess it depends on how far the car is coming apart and what you want for the dollars expended. The right 275 section width tire can give some good grip for turning but with 600hp on the street it can come out fast. If you don't want or don't plan on stripping major amounts of undercoating then your plans are good.