Hello, I worked in a truck shop in Oklahoma city for a couple of years and we shortened and lengthened many a big truck frame. All we ever did was square cut them. It is so much easier to get your measurements correct and square and all of that when you square cut it. We did glove the frame atleast 12" each way from the weld and then weld and bolt all of it togeather. Never had a issue with any of them. Heck on some of the Macks they were already gloved so we would put a triple glove in them.

The diamond fishplate is kinda the standard except we would usually not have the diamond come togeather on the horizontal end if you can understand that. I have been welding for a living since around 88