I've been a welder for 25 years, I do not step cut a frame I shorten, however, I do weld both the inside and the outside of the frame rail at the joint, and I add a fish plate on the inside of the frame. A fish plate is a diamond shaped piece of metal the same thickness as the frame rail. The Diamond shaped piece is positioned centered over the weld joint, with two points being up and down and the other two points at the center of the frame height. The diamond is fully welded, with the welds all running at about a 45 degree angle. If I have cut a channel shaped frame rail, I will also enclose the back side of the channel, often using the piece I removed, centered at the cut line. This process reduced the chance of creating stress cracks a step cut can create from the corners of the angles.

Step cutting the frame isn't real difficult, it just requires close measurements. You make a vertical cut from the top to about 1/2 the height of the frame, then a horizontal cut of 3" - 4" long, then make the vertical cut from the bottom up to join the horizontal cut. Then you do an identical cut at the distance of the material you are removing. What you need to be careful about is to be sure when you make your intersecting cuts that you don't cut past your lines and create a place for stress cracks to start. Clean up the edges, clamp the material together, and weld the step cut on both sides. Gene