I am researching options for improving my intake/exhaust setup and need some clarification. Right now I plan on using an Offy 2 carb intake with Fenton cast header. I was going to use Hedman tube headers, but I was informed that they tend to rust/leak really fast. As far as the Offy is concerned, a friend told me to use 2-2BBL "progressive" carbs instead on 2-1BBL carbs. I however have no idea was a progressive carb is. Can someone enlighten me on this matter. Also, are there any particular carbs that should be used?

thanks
jf
1966 C-10