Hooker makes a two inch primary tube diameter header for the SBC and the 1965-70 Chevy full size car but it is a competition style header.
A competition only header means no flanges on the end of the adjustable length collector to cap it up, and many of the tubes are slip fit and not fully welded so you can easily remove the headers for engine maintenance or R&R (you don't worry about exhaust leaks when you are running uncapped). Another count against them is they are made of light gauge tubing and have light weight (thinner) flanges to reduce weight which is good for racing but bad for the street as the flanges will warp faster (more exhaust leaks) and the tubes won't last long if they ever get wet.
I believe you can get up to a 2-1/8th inch tubing from most header manufactures for a full all out race header. As when racing you don't worry about bottom end torque because you leave at 5000 RPM and shift at 7,800 RPM so who needs bottom end anything; it is all about WOT performance. Now if you want to drive this car on the street then I would think a 1-3/4 inch header would be as big as you want to go unless your running a stroked 383-406 in which case a 1-7/8 inch would be my maximum size. These can be found in thermal coated, long tube, three inch collectors with flanges with heavier 1/4 inch thick flanges to maintain a tight seal.
Just be sure to read all of the foot notes (that string of two or three digit numbers after the part description) at the bottom of the catalog page to be sure your car isn't the exception to the guaranteed great fit.