First, let's recognize your friend has a cool car that is a hot set up. It is not just the newer motor, but the new transmission with 2 overdrives that allow low end gearing without giving up drivability. Worse yet, the 69 Camaro started out as a lighter car than your Challenger, and the modern LS engine and 6 speed transmission are both going to take even more weight out of the Camaro. All the new motors can make lots of power while enjoying good fuel economy and low maintenance. But before we get all depressed, remember that it cost your friend some significant bucks to do the engine & transmission swap. If you spend the same type of money on your car, it will be competitive. He will always have the advantage of a lighter car. If he has modded the LS engine and you want to catch him, probably time to start thinking about how to add displacement. That is where you have a big advantage, with a big block engine you can make lots of power by reaching displacement levels not available with the smaller modern engines. Cubic inch for cubic inch, the LS has thousands of dollars of electronics on its side and that won't be easy to beat staying at 383 displacement, especially against a lighter car with lower gears.