my 2 cents
4020 tractors esp with loaders saw a fair amount of frame rail replacement this is not uncommon. Usually it was from lack of not checking the bolts from time to time and they got loose and damaged the rails. Definatelly go with aftermarket rails for the price but like the others said use JD hdwe to go back together. There are 2 different lengths available in the std size bolt. Std bolt is p/n R31505 5/8 x 1 5/8. Longer bolt (not in parts catalog) p/n r47953 is just over 2" long with about 1/2 extra threads. If needing to go larger the oversized bolt is p/n r73383 and is a 3/4 by almost 2" long bolt. There also used to be a repair kit (sleeve assy type unit). But that p/n is escaping me at the moment I think it brought you back to 5/8. Good luck
4020 tractors esp with loaders saw a fair amount of frame rail replacement this is not uncommon. Usually it was from lack of not checking the bolts from time to time and they got loose and damaged the rails. Definatelly go with aftermarket rails for the price but like the others said use JD hdwe to go back together. There are 2 different lengths available in the std size bolt. Std bolt is p/n R31505 5/8 x 1 5/8. Longer bolt (not in parts catalog) p/n r47953 is just over 2" long with about 1/2 extra threads. If needing to go larger the oversized bolt is p/n r73383 and is a 3/4 by almost 2" long bolt. There also used to be a repair kit (sleeve assy type unit). But that p/n is escaping me at the moment I think it brought you back to 5/8. Good luck