McMaster Carr is amazing, they are just so expensive usually. I like your vision in incorporating the chain throughout the bike. Rear fender struts, license plate bracket, brackets for footpegs, it has endless possibilities. I wouldn't do everything in chain but tastefully throughout would be sweet!! A formed seat made out of coiled chain would be insane, not to comfy for long rides, but for a bar hopper, frisco bobber it would be a new touch.