The frame when new was more than enough for a big block, but after 50 years of flexing it needs some help. I would at least box the front end area and the section over the rear axle. One word of advice is do only 1- 2" welds spaced at 6" apart. Let it cool for several hours to hand touch. Then do 1-2" welds in between that and so on. You will warp the frame if you get to quick and run beads longer than 2". Its a real PIA to get it back again. Don't ask how I know that.
