I measured where the square tubing was located on the bottom frame. Make sure and grind down the welds and use a square to scribe lines on the frame to help locate the square tubing. The upper bars can only go on one way. I used a torch and cut the floor from the square tubing I was going to cut out. You can use a grider and cut the welds on the floor and pull it away but cutting it looked alot easier and I don't expect this to be the last time I will ever reclip one of these things!
I used the torch and cut the tubes. Make sure and do this on the side you are cutting off ( I know this is obvious but it is easy to screw up, Trust me) and be carful not to burn through the good bars. You can use a saw for this also. Now for the real fun part, all the grinding. Grind off all that is left of the old bars. There are 2 bars that run down the center of the frame at the bottom that you need to be carefull with. I ground down all the welds on the top and sides to where I could see a line of where the old square tubing met up with these bars. Take a chisel and split the break to get the piece if steel left off of the old square tubing, this will leave the ends of the tubes open.