early A body exhaust EXPERTS!

Single exhaust IMO is the better way to go on a small cube motor, headers or not. ...but the OP asked about duals. I like single exhaust on small cube motors because you can really build a great scavenging system. That's how I'm doing my 318 in my truck. 2.5" pipes off the headers into a flowmaster "Y" and then into a single 3" pipe. It works well.