Not trying to tell you what to do but the best thing is to put a good weld, then grind the inside of the frame down flush. Go to a metal shop and have them bend you a piece to go inside the frame have it go as far as you can on each side of the weld. you should use 3/16 or 1/4 inch plate your frame should be 3/16, don't use anything any thinner though.You want the inner frame to be a tight fit, after you put it in do not weld it,that will cause your frame to brake. Bolt it on each side of the weld, use grade-8 bolt 1/2 in will be good for that. That will fix your frame and you want have any problems with it.I'm a welder/mechanic and this is how you cut semi-trucks and put them together, I've done alot of the.Hope everything works out good for you.
