the 06 Dyna was the first model with O2 sensors and the rest followed in 07-10. the popping on decell is caused by a lean condition. We deal with it every day when someone wants a free flowing exhaust. using the stock mufflers on a crossover system is a great idea. We have set up many police bikes with this combination and the police motor officers stay in touch with us commending us for the increased power without making the bike illegal. This was on bikes from 08 and earlier. Using the stock head pipes is OK but it is a detuning effort. True duals are for more flow for each cylinder. I hope this helps some of you about stock vs true duals and what years efi were implemented for all models.
JR
JR