How far are you going to go with building your engine. If you plan on a beast then yes, I would go with Hooker Super Comps or Heddman Elites or something. However, if you are keeping it relatively stock (perhaps say... intake and carb, ignition upgrades only, maybe small cam, etc).. i would say don't go too extreme with the headers and get Tri-Ys or some smaller headers. Big headers on an engine not built for them will lose you power, since the advantage of big headers come at high rpms (rpms that a stock or near stock engine will never reach). Big headers also move your torque up (and sometimes out, again if your engine doesn't rev that high) the rpm range.
So, as with all engine parts, you must plan ahead. And as long as there are no cracks or holes or excessive rust on the headers, ebay would be fine.
Edit: Looking at your engine, I would buy Hooker Comps, not Super Comps. They'd match your engine well.