I agree with rushking. You don't want back pressure. In fact it's a misnomer used by old hot rodders in the 40s and 50s that didn't understand fluid dynamics. (air acts like a fluid inside of a pipe) They just knew that a smaller pipe yielded better results in very specific low to mid RPM applications but couldn't explain why that was the case. What you want is exhaust velocity to help with scavenging where they meet at the collectors, merge and X pipes in the exhaust system.
Will the dual exhaust work? Sure it will. Is it the most efficient? Probably not. That depends entirely on the number of cylinders, the firing order, and how evenly the ignition events are per bank.
If you do opt for the dual exhaust you really want the X pipe because it helps a great deal when you have less than 4 cylinders on a single side of the exhaust. Our firing order is 1-2-3-4-5-6 with bank1 having 1-3-5 and bank2 having 2-4-6. This means you have one cylinder firing exactly every 120 degrees of crank rotation then if you divide the block by it's two banks for a true dual exhaust, you have an even spread of a cylinder firing exactly 240 degrees of crank rotation per bank. That's a big spread between ignition events on one bank which reduces the effectiveness of scavenging on a true dual exhaust. At least on a 4 cylinder (or a single bank of a V8) you have one ignition event every 180 degrees of crank rotation that is far better for scavenging than a single bank of 3 cylinders.
Our firing order, separation of banks and even spread of ignition events is also great because if we wanted to run a twin scroll turbo on the 2.7L it would work perfectly. We could separate bank1 and bank2 leading into the two halves of the twin scroll turbo without an overly complex header setup.
The 2.7L Delta sweet spot for primary tube sizing is between 1.63" and 1.75". The smaller 1.5" primaries of the ebay Chinese headers seem to work really good on a N/A car but falls on it's face up above 7000RPM because it's too restrictive. The rest of the catback after both banks merge together seems to range between 2.125" and 2.5" depending on the manufacturer. Larger isn't always better, but once you are past 18" after the last merge/collector it doesn't matter as much how big it becomes. However, if you have an X pipe on your dual exhaust, you need to maintain the same pipe diameter from the last merge/collector all the way through the X pipe and at least 18" after the X pipe.