You won't find a better street carburetor than a Quadrajet. You'll need to get it rebuilt by someone who knows them and can set it up properly for the 350HO...different cam specs can make for different jetting requirements. If the new engine came with an intake for a spread-bore carb like the Q-jet, you should be fine. If you need an intake, get an Edelbrock Performer or equivalent from Weiand or other quality supplier.
If a Q-jet is not available, my own preference would be an Edelbrock Performer carburetor...they're simple, easy to adjust and maintain their adjustments. Get a Performer 600 or 650 with electric choke and you should be quite happy. Get either an Edelbrock Performer or Performer EPS intake (the EPS is made strictly for a square-bore carb and is optimized for them).
After that I would choose a Demon or Holley carb...preferably the Demon. If you plan on racing the car, they may be better choices, but for the street and street performance, I believe the Q-jet and Edelbrock are better.
For whatever brand headers you buy, don't use wrap on them...that will void the warranties and supposedly promote rust. Get ceramic coated...it costs a bit more but will last longer, maintain its looks better and help with the heat.
As far as what brand headers, I like Sanderson, but there's lots of good brands. You first need to decide what design headers will do what you want. Block hugger headers fit well, don't hang close to the road, but don't give max power. Long tube tuned headers provide more power, but often cause clearance problems. Tri-Y headers increase torque, but again, can create clearance issues. Figure out what characteristics you want and then decide what style headers best suit that...then find the brand that best fulfills that.
These are all my less than objective preferences...someone else may well disagree or have their own preferences, which is fine. As I said...you have to decide what you want out of the car, then determine what mix of parts will accomplish that. Mixed parts that work in unison will do you better than a lot of expensive parts not matched and end up working against one another.
