LSA or Duration to fine tune glasspacks??

Don't buy them for their handsomeness.Buy them for what they do to the sound. Before you weld them on, do a slip-fit test to see,rather hear, the difference.
But before that;
If you have the resources, you might also try a swedged pipe to convert what you have now, to a 3inch round outlet. The pipe should be about 15 inches long. Then slide it up and down your pipe, to tune it. Stop when you like it. You kindof have to do both pipes to get the stereo effect. When you are finished that,crush them down to oval, and start again. I like ovals.