They will fit (check the foot notes about A/C and power steering. When you get to a primary tube of that size you are going to have fitment issues and the headers were not made to fit your car, but a Camaro, then a Chevelle and oh yah you can hang them off of the heads in an Impala as well (they will almost fit under the hood of a light truck also, but the collector hits the toe boards as the motor is higher up for ground clearance in a truck).
This is the problem with a universal header, it universally fits nothing exactly. The header company wants only one part number for small block Chevys, one for all big block Chevy engines, one for small block Fords one for all Coyote Ford engines, one for all big block (385) Fords, and one for all Chrysler V6 engines, etc. to reduce inventory. You have to make your own by buying a kit and having your local welding shop weld it up just like it was back in the early sixties if you actually want to get headers that fit.
Personally I think a two inch primary is too big for a 396 and a Headman 1-7/8th inch primary would be a better choice. They will drop in in without any drama or dinging pipes to clear in my experience.
If you want big tubes (for a future bigger big block (such as a blown 540 or a 632) try this kit:
It is what I used on my 582 (I used the stainless steel kit instead of mild steel tubing to prevent it ever rusting, but it was this size primary).
Every header company offers a kit in milkd steel most also offer one in stainless (which requires a TIG welding machine, a lot of Argon gas, and an experienced TIG welder tech to get a seamless finish suitable for polishing).