Here's what comes to mind: notch it for some shallow C-channel welded longitudinally, maybe 3/16" wall if you want to be burly, then plate the sides as well with 3/16" plate. It will NOT fail. It will likely be much stronger than the other side in fact. If you are still nervous, take some more of the C channel and cap the top of the frame (in line with the frame), with a 45* cut in front, and box it in at the front, effectively 'raising' the frame a bit. Stitch weld if you are nervous about distortion, but I highly doubt it will be a factor.

A plasma cutter would make short work of it. I don't know how I got through projects without one (one of the new, very nice dual voltage Millers). Between that, and a HF metal bandsaw, making a nice step bumper for my son has been a piece of cake +/-. Both gifts from my lovely bride. <img src="/forums/images/graemlins/kewl.gif" alt="" />