looks like a fun project. Unfortunately Racks will not make the bike any stiffer. I doubt that a bike like that would turn into a flex noodle once you add panniers and load. I would highly recommend some type of "hands on" type of shifter upgrade. Going from downtube shifters to stem shifters would not be much of an upgrade. ( you still will have to ride one handed when shifting, so shifting when you are off of the saddle will still not be possible).