K member & 400 B Big Block question.

Hey all, I just bought a 1967 Barracuda that started life as a slant 6 but was converted to a 318. I know there’s a difference between slant 6 and V8 K members but, is there a difference between Small Block and Big Block K members? I’m looking to build my 400 and run it in my Barracuda but was asked if the K members were different. Also does anyone know if the stock 400 crankshaft is good to run 400+ hp? If not what crankshaft is there to run without making it a stroker motor.