I have researched this for a while now and so far I have not been able to find fenderwell headers for any engine (SBC, BBC, or W) in a 55-59, 60-66, or 67-72 GM pickup.
Just a thought , but you might want to check out the 2 inch primary fenderwell exit BBC headers sold by Speedway Motors. They're about $200, I am adapting a set with 409 flanges to use on a 527 inch W-motor stroker in my 37 Chev truck.
I'm a little confused This started as a search for fenderwells for a TRUCK with a sb, now it's about BB car headers are they supposed to be interchangable or something?