I've got a 4" King Cobra and a 4" Smith & Wesson Mod. 66- the only difference is the full underlug on the Colt vs the partial underlug on the S&W.
As for differences- the Colt is coil springs, the Smith is a leaf spring. The Colt turns clockwise, the smith turns counterclockwise. The Colt cylinder release pulls back, the Smith pushes forward.