Frame Support

My 71 chevy pickup is the first of many long bed to short bed conversions I am wanting to do. I am wondering what would be the best way to make the frame stronger were the cut is? Keeping in mind I do not want to see anything from the outside of the frame rail. So the frame looks as stock as posable.

Streets told ya right, if you want to be double sure, you could box the inside with a peice of flat the same thickness as the original rail and about 12" long.