Those are two different bikes.
The mufflers aren't the only components that are different.
Check the seat, heatshield, rear shocks, turn signals, rear wheel and brake, footrests....
The only similarity is the color of the gas tank and rear hump.
Someone once gave me an old BMW airhead suppertrapp, which I put on my R100. It was really loud even with a reasonable number of plates.
Then I discovered that there was no internal pipe or glass packing in it. It was on a track bike and had the internals removed to make it lighter (I guess).