[rodneym]

Make sure you check out some books with a complete history of Cobras. The 'slabside', 289, FIA, 427 (SC and street versions) and engines.
When I bought my SPF, which was a great car, it had a small block. Didn't think it was important. With time, it became important! Be honest with yourself. Are you the type of guy who really gets into things? You can get big block power from a small block AND reliability and low maintenance with a big block. I don't think anybody really needs one over the other. Unless you're a purist, or ask that knawing feeling inside...
But with a budget of 30k your options will be a bit limited, again, depending on what you want. But make sure you know what your looking for first. I don't mean to sound like a holistic nut, but if you 'put it out there', something will come around in time. And don't short change the step you're at now. It's a fun one. I'm on my 3rd Cobra and I keep on looking just for fun. Plus, mrmustang and a few others seem to know a lot about the used market and they've been at it for a while.
Good Luck,
rodneym