Im done screwing around with the extended "Model A" frame I have under my 24 dodge roadster. I extended it by butting it with 2x4 box beam and welding plates on top of the welded seams all the way around it. My problem is it keeps on cracking out every weld. I dont know if its the old steel, my cruddy welding or if the 318 was just to torquey thats doing it.

Im building a new frame tomorrow since I dont have to go into work. Should I use more 2x4 box beam or that 2x4 u shaped channel?