I have found that those "cherry bombs" mufflers do the trick.
Keep your mufflers now and by the fuel tank where the tail pipe runs, you do have those right, cut it with a hack saw and fit in a 2 1/2 or 2/14- what ever the tail pipes are-around a 16 " long straight "cherry bomb" muffler. They cost like $20 each, then stick a straight pipe in till in just passes the bumper.
It really helps out and I don't believe it chokes it up that much. Cheap, easy to do and even last a long time, believe it or not.