Can you get your hands on an infrared heat gun to shoot engine/radiator/hoses and see what your temps really are? Like Barb said, are you sure the t-stat was put in the right direction with the element down into the manifold? Probably is, or you would be tending to run hot, then snap open once the whole housing got hot enough...(I think). Was the "new radiator" an OEM replacement, or did you put in something custom? Be sure the path from the filler neck to the coolant recovery tank is not blocked or you can get a vacuum lock on the system. New hoses with the new radiator? Bottom hose is not sucking closed is it? I lean towards air in the system - some Jeeps need to be parked on a steep uphill slant and vented (pressure off the system) to get the air out of the intake - never heard of it on a SBC though.
I've seen that there were lots of problems with deteriorating intake gaskets due to DexCool, which might explain your leak, but not your temperature issue.
http://www.consumeraffairs.com/autom...m_dexcool.html