Lightening your K frame
My 2 cents:
That flange you want to shave off, and replace with melted welding rod adds significant stiffness to the part. I would not trim any of it. The K member resists all the torsional forces exerted from front suspension, and engine.
If you want to make a stronger front end, reinforce the lower cross member running under the radiator, and find something that is nonstructural to put on diet, such as a back seat, a spare tire etc…
You may want to compare the weight of melted rod vs. metal trimmed. I bet it is almost a trade-off.