I thought headers and duals went hand in hand. This is the first time I've ever heard of someone wanting, or having headers and wanting single exhaust. Going for the stock exterior look?
Best of luck with the radiator. You don't really want that lower hose taking that route, and you'd have to cobble something together to make work. What condition are your 3 rads in? Might be worth taking one into a rad shop, they should be able to change the location of the lower port. It will be a decent amount of work, but worth it. I'll never know why they ever had that radiator design, with the ports on the same side. You get much better heat transfer with one left, one right, top or bottom. This gives you "cross flow". The one you show, the side without the ports, isn't doing alot of cooling.