Header explanation? Please

Equal length - better scavinging of the exhaust, per cylinder. The other cylinder that just fired, and is moving exhaust out, pulls the next firing cylinder exhaust out with it. And less restriction than an iron manifold, that was made just to clear everything.
36" is a start. Put 18" extensions on the header, sprayed with rattle can paint. Make a full run and kill engine. The point that the paint stopped blistering off is the optimum length the current engine wants. cut the pipe there.
! 7/8" = more torque. More = single plane, all rpm to use, like a 350 chebby. Mopars win with the torque with the longer stroke, and close to squared bore/stroke. Torque usually wins.
Unless all-out pro stocker, 1 7/8", tune the extension.